Predicting the 20 Most Expensive Transfers of the 2015 Summer Window

Here are predictions for the 20 most expensive signings of the 2015 summer transfer window.

These 20 footballers, including the likes of Gareth Bale, Ilkay Gundogan and Memphis Depay, will be ranked according to their estimated transfer fee.

The estimated transfer fee is determined subjectively based on performance this season, potential ability, hype and stock.

Honourable Mentions

German central midfielder Johannes Geis, 21, Mainz | Estimated Transfer Fee: €19.5/£14.4 million.

Ghanaian left-back Abdul Rahman Baba, 20, Augsburg | Estimated Transfer Fee: €19/£14 million.

French left attacking midfielder Yannick Ferreira-Carrasco, 21, Monaco | Estimated Transfer Fee: €18.5/£13.6 million.

English centre-forward Saido Berahino, 21, West Bromwich Albion | Estimated Transfer Fee: €18/£13.3 million.

Swiss goalkeeper Roman Burki, 24, Freiburg | Estimated Transfer Fee: €17.5/£12.9 million.

20. Ilkay Gundogan (Borussia Dortmund)

Estimated Transfer Fee: €20/£14.7 million.

German central midfielder Ilkay Gundogan, 24, has signalled his intentions to leave Borussia Dortmund by refusing to extend his contract.

Lingering doubts over his long-term fitness, average performances and his free agent status in 2016 means you should expect Borussia Dortmund to sell Gundogan in the summer transfer window before his Bosman rights can be exercised.

In the Bundesliga transfer market, €20 million is a substantial investment, but nowadays it is a price you see major clubs pay for squad players.

Gundogan is currently placed at No. 114 out of 203 footballers in Kicker's Bundesliga player rankings.

19. Allan Marques (Udinese)

Estimated Transfer Fee: €20/£14.7 million.

Udinese's Brazilian central midfielder Allan Marques, 24, is one of the best footballers in Europe. 

However, Udinese need to lock Allan down because his current deal runs until 2016.

If not, he will be leaving this summer window before he is eligible to exercise his Bosman right to a free transfer.

Allan is a complete footballer who is a ball-winning machine and has made significant gains when he is in the attacking half.

Think Arturo Vidal circa Bayer Leverkusen.

18. Jordan Amavi (Nice)

Estimated Transfer Fee: €20.4/£15 million.

Nice's French left-back Jordan Amavi, 21, is a legitimate alternative to Ricardo Rodriguez, whose transfer value could be too pricey for potential suitors.

Amavi is forceful and at times a gung-ho defender.

This leads to him winning back the ball at a frenzied rate (4 tackles and 4.5 interceptions per 90 minutes), though he is an easy target for yellow cards (four successive bookings and counting).

17. Morgan Schneiderlin (Southampton)

Estimated Transfer Fee: €23.1/£17 million.

Southampton's French central midfielder Morgan Schneiderlin, 25, is an all-round Premier League-proven footballer. 

A sturdy tackler and a passing outlet, Schneiderlin was at times a goal threat. This suggests he can play as a No. 6 and a No. 8. 

What could adversely impact Schneiderlin's transfer stock is rehabilitating from a knee ligament injury, which might sway Southampton to field offers for his signature.

16. Salomon Rondon (FC Zenit)

Estimated Transfer Fee: €25/£18.4 million.

FC Zenit's Venezuelan centre-forward Salomon Rondon, 25, could be a backup No. 9 target for major clubs. 

Rondon can finish with either feet and is an aerial threat. 

He has scored 11 goals from 23 Russian Premier League games this season, which is impressive when you consider he has only started 65.2 per cent of games he has been involved in this season. 

However, there are concerns over Rondon's consistency as he tends to go missing for stretches of the season.

In addition, he was wayward in the UEFA Champions League, scoring once and shooting on target 22.2 per cent of the time.

15. Yacine Brahimi (Porto)

Estimated Transfer Fee: €27.1/£20 million.

Porto's Algerian left-forward Yacine Brahimi, 25, is a mercurial take-on specialist.

He provided instant impact during Porto's UEFA Champions League campaign, scoring five goals and providing three assists in nine games.

Given Brahimi is approaching his late 20s, Porto need to decide if he can replicate his UEFA Champions League heroics next season.

If not, cash in before Brahimi is exposed as an erratic and inconsistent highlight reel player.

14. Felipe Anderson (Lazio)

Estimated Transfer Fee: €30/£22.1 million.

Lazio's Brazilian right/left forward Felipe Anderson, 22, needs to thank Filip Djordjevic.

Pressuring Massimo Gobbi into a mistimed clearance, Djordjevic retrieved the ball and played in Anderson for an easy tap-in during Lazio's 2-1 win over Parma.

It had taken Anderson 12 games to score his first Serie A goal of the season. 

Since then, Anderson's class is why he's separating himself from the rest of the players on the field.

13. Paulo Dybala (Palermo)

Estimated Transfer Fee: €33.9/£25 million.

It is a matter of when, not if, Palermo's Argentine centre-forward Paulo Dybala, 21, will be sold in the summer transfer window. 

Dybala's relationship with Palermo president Maurizio Zamparini is damaged, which suggests sentiment will play no part in keeping the burgeoning star.

Dybala has scored 13 goals and provided 10 assists in 33 Serie A games this season, though his inconsistency is still a red flag. 

Remember, he was a bust entering this season.

12. David De Gea (Manchester United)

Estimated Transfer Fee: €33.9/£25 million.

Manchester United's Spanish goalkeeper David De Gea, 24, is better, younger and an upgrade over Iker Casillas.

Hypothetically speaking, it makes sense why Real Madrid would want to replace Casillas with De Gea.

• Once-in-a-generation goalkeeper.
• From Madrid. 
• Natural successor to Casillas.
• Has La Liga experience having played for Atletico Madrid.

De Gea's hesitancy in extending his contract at Manchester United could foreshadow a big move to Real Madrid.

11. Santi Cazorla (Arsenal)

Estimated Transfer Fee: €35/£25.8 million.

Arsenal's Spanish midfielder Santi Cazorla, 30, still has re-sell value. 

He is a crafty footballer able to play as a No. 6, No. 8, No. 10 and No. 11.

Scoring seven goals and providing nine assists from 33 Premier League games this season, Cazorla has been a contributor to Arsenal.

He has been playing at an elite level since his Recreativo Huelva days.

Aleksandr Hleb, Emmanuel Petit, Kolo Toure, Marc Overmars, Thierry Henry and Thomas Vermaelen are examples of Arsenal manager Arsene Wenger offloading experienced footballers before their transfer stock diminished.

10. Memphis Depay (PSV Eindhoven)

Estimated Transfer Fee: €40/£29.5 million.

PSV Eindhoven's Dutch left forward Memphis Depay, 21, is Cristiano Ronaldo-like in the Eredivisie.

Memphis shoots from all angles, he dominates opposing Eredivisie defenders and is a quasi-No. 9.

Scoring 21 goals and providing four assists from 28 Eredivisie games this season, Memphis should be on the radar of most major clubs.

9. Mats Hummels (Borussia Dortmund)

Estimated Transfer Fee: €40.7/£30 million.

Jurgen Klopp calling time on his Borussia Dortmund tenure provides a natural exit route for German centre-back Mats Hummels, 26, who has been at the club since 2009.

Injuries, Borussia Dortmund falling apart and Hummels constantly playing catch-up is why he was not at his best this season.

Hummels is currently placed at No. 65 out of 203 footballers in Kicker's Bundesliga player rankings.

A major club will bank on Hummels' body of work rather than his recent form.

8. Roberto Firmino (Hoffenheim)

Estimated Transfer Fee: €40.7/£30 million.

Hoffenheim's Brazilian central attacking midfielder Roberto Firmino, 23, has regressed this season.  

Firmino has the technical ability of Ronaldinho and the daring nature of Djalminha.

There is more talent in Firmino's toe than in Thomas Muller's entire body. Yet Muller is a serial winner, a high football IQ player and dependable.

For whatever inexplicable reason, Firmino will go missing for several games, then rectify it with a world-class performance.

Firmino's extraordinary upside should see a suitor lodge a substantial bid, even though there are red flags with his concentration and inconsistency. 

He is currently placed at No. 49 out of 203 footballers in Kicker's Bundesliga player rankings.

7. Ricardo Rodriguez (Wolfsburg)

Estimated Transfer Fee: €45/£33.2 million.

Wolfsburg's Swiss left-back Ricardo Rodriguez, 22, has all the attributes of a world-class footballer. 

Big motor, set-piece specialist, plus he is productive in the attacking and defensive half. 

Backed by Volkswagen, Wolfsburg don't need the cash, but here is a hypothetical scenario:

• Sell Rodriguez for €45 million and invest in Abdul Rahman Baba, who could catch up to Rodriguez in terms of development. 
  
• During a seven-game run in the Bundesliga, Rodriguez was out for five games due to injury. 
• His defensive positioning at times is lax. 
• Currently placed at No. 44 out of 203 footballers in Kicker's Bundesliga player rankings.

6. Granit Xhaka (Borussia Monchengladbach)

Estimated Transfer Fee: €47.5/£35 million.

Borussia Monchengladbach's Swiss central midfielder Granit Xhaka, 22, could develop into one of the best footballers of his generation.

From the outspoken outsider who once criticised the Borussia Monchengladbach dressing room, Xhaka now leads by example.

Persistently putting his body on the line is why Xhaka is a dominant presence in midfield

When he is in possession, he is a passing outlet. 

He is a big reason why Borussia Monchengladbach are the third-best team in the Bundesliga this season.

Xhaka is currently placed at No. 34 out of 203 footballers in Kicker's Bundesliga player rankings.

He is outperforming the rumoured €20/£14.7 million release clause in his contract, which comes into play in 2017, per Stephan Uersfeld at ESPN FC.

5. Alexandre Lacazette (Lyon)

Estimated Transfer Fee: €50/£36.9 million.

Lyon's French centre-forward Alexandre Lacazette, 23, is young, he scores, creates, gets past defenders and is one of the most productive footballers this season.

He has accumulated 33 total goals (27 goals, six assists) in 31 Ligue 1 games.

Barring a career-debilitating injury, you should expect Lacazette to become a valid challenger for the European Golden Shoe when he moves to a league with a higher coefficient ranking.

4. Raheem Sterling (Liverpool)

Estimated Transfer Fee: €54.3/£40 million.

Liverpool's English centre/right/left forward Raheem Sterling, 20, has all the characteristics which suggest he will be an inflated transfer:

• English.
• Overhyped.
• Potential over productivity.
• Embroiled in a contract dispute.

Sterling's seven goals and seven assists do not substantiate whatever ludicrous wages he is demanding. 

But he has a valid counter-point to his inconsistency: He has been shifted all over the field.

If Liverpool cannot resolve Sterling's contract issues, then he will be offloaded to the highest bidder.

3. Koke (Atletico Madrid)

Estimated Transfer Fee: €61.1/£45 million.

Atletico Madrid's Spanish left winger/central midfielder Koke, 23, is a world-class midfielder.

If you are judging him as a midfielder, he has no flaws: Wins back the ball, is an incisive passer, can play in multiple positions and is tactically disciplined. 

To Sheik Mansour, €61.1 million is the equivalent of a $50 dollar note to the man on the street.

Assuming Manchester City want to revitalise their ageing and underperforming squad, Koke should be one of their top summer transfer window targets.

2. Kevin De Bruyne (Wolfsburg)

Estimated Transfer Fee: €67.8/£50 million.

Wolfsburg's Belgian central/left attacking midfielder Kevin De Bruyne, 23, is prone to turning over the ball, but he is a centre-forward's best friend.

De Bruyne can make every pass in the book and he is willing to take risks to get his assist. 

Just imagine a De Bruyne-Sergio Aguero partnership at Manchester City.

De Bruyne is currently placed at No. 3 out of 203 footballers in Kicker's Bundesliga player rankings.

1. Gareth Bale (Real Madrid)

Estimated Transfer Fee: €88.2/£65 million.

Welsh right forward Gareth Bale, 25, is on course to be the biggest waste of money in football history. 

Nine players have outscored (14 goals plus) Bale (13) in La Liga. In terms of assists, again nine players have provided more goals (nine plus) than Bale (eight).

Bale's defending has deteriorated drastically (quite sad considering he was once a left-back with elite upside), and he is too reliant on kick-and-run. 

Look at Lionel Messi, Neymar and Luis Suarez—they play for each other. 

Whereas Cristiano Ronaldo wants his team-mates to play for him only. Bale is a luxury player who takes away goals from Ronaldo.

Their relationship will only function if Bale creates for Ronaldo in his quest to be the Pele of his era.

Before Bale's transfer stock takes an irreparable hit, Real Madrid should cut bait and hope a Premier League club is willing to gamble on his past performances for Tottenham Hotspur.

+allanjiang.

When not specified, statistics via WhoScored.com.