Inigo Martinez had a great season for a Real Sociedad side that finished fourth in La Liga.
Despite signing Cristian Zapata on a permanent basis earlier this year, Milan is still in need of a new centre-back.
With Mario Yepes' contract expiring and Cristian Zaccardo not expected to be back at the San Siro for next season, the Rossoneri are very thin at the centre-back position.
Massimiliano Allegri has just four centre-halves to choose from should the position fail to be addressed in the transfer window, and they include Philippe Mexes, the aforementioned Zapata, Daniele Bonera and Bartosz Salamon.
Bonera is 32 and little more than a bit part player, Mexes can struggle with consistency at times and Salamon hasn't made an appearance for Allegri's side since joining in January.
Zapata's pace makes him an asset to the first team, and if one were to project Milan's starting central-defensive pairing for next season, it would include Zapata and Mexes, who had a solid season last term.
Milan has adopted a transfer policy of attempting to buy young and talented players, develop them and eventually integrate them into the first-team.
The four players on this list are all 22 and under and have shown the potential to develop into very good centre-backs. Kurt Zouma, Eliaquim Mangala and Kyriakos Papadopoulos, just to name a few, have been left out because their transfer fees would likely rise so high that it wouldn't be feasible for Milan to target them.
Most of the following players have not been formally linked with a move to the San Siro outfit, so this is speculation, but all look to be burgeoning stars and therefore should be targeted.
Let's take a look at four centre-backs Milan could target to shore up their back line for next season.
21-year-old Bruno Martins Indi made his first-team debut for Feyenoord back in 2010 when he was just 18 years old.
Since then, he's gone on to make 74 appearances for the Dutch side, and his performances at club level earned him call-ups to both the Netherlands U-21 side and the senior team.
He's made seven appearances at the U-21 level and was recently in Israel for the UEFA U-21 European Championships, where he made played the full 90 minutes in three matches, including a semifinal match against Italy.
Quite surprisingly, BMI has actually played in more games for the senior Dutch squad. In his nine matches for the Oranje, he's scored twice and looks to have a long future for a national side that has had their fair share of defensive struggles in recent history.
Martins Indi accumulated just three bookings in 32 matches last season, quite a low number for a centre-back and one that speaks to safe, efficient tackling.
At nearly 6'2", he has the height to cope with an aerial threat, getting up well to parry opponents' crosses.
He's a good passer of the ball and is able to keep possession well, perfect for a Milan system that led Serie A in possession last season.
Like Zapata, BMI has a good bit of pace for a centre-back and has the requisite strength to deal with some of the Italian top flight's more corporeal centre-forwards.
He can struggle at times with positioning, but at just 21 years of age, he will have plenty of time to break his bad habits. The Dutch starlet can also play at left-back, though he was utilized predominantly in the centre of defense for a Feyenoord side that finished in third place last season.
Milan have been linked with the Netherlands international, though an official bid is yet to be lodged, according to Algemeen Dagblad (h/t Goal.com). It could take around €9 million to prize the centre-back away from his boyhood club, but one option to lower the fee would to be include compatriot Urby Emanuelson in a swap deal.
The 27-year-old Emanuelson has struggled to break into the starting XI at Milan, and the opportunity to return to his home country for the hope of consistent first-team action could pique his interest.
After being relegated in the 2011-12 season, Villarreal earned promotion back to La Liga following a second-place finish in the Segunda Division. Their 22-year-old Argentine defender, Mateo Musacchio, played a huge part for the Spanish side, who allowed 38 goals in 42 league matches last season, good for second-best in Spain's second division.
Since 2010, Musacchio has made 107 appearances for Villarreal, and his performances also earned him a call-up for Argentina, which he parlayed into two caps.
He isn't the biggest defender, standing at just 6'0", and can struggle in the air, but the other aspects to his game more than make up for it.
He's a leader and has a high football IQ, two qualities that have allowed him to play beyond his years. He's an efficient tackler, but by far his biggest strength is his ability to read the game, as he can readily be seen intercepting passes before the ball can be played to the oppositions' forwards.
That intuitive ability to quell a threat is something that has made players like Thiago Silva so successful.
After choosing to stick with Villarreal despite their relegation, Musacchio could be inclined to stay with Spanish side after he helped guide them back to La Liga.
He hasn't been formally linked with Milan, but he's of the proper age and ability level to fit into Milan's transfer policy. Musacchio has just one year left on his contract, meaning he could be available at a cut price.
A bid of €5 million could be enough to force Villarreal's hand, and Milan would be getting a cerebral footballer with great potential for a very reasonable fee.
Martins Indi's central defensive partner at Feyenoord would also be a great option for Milan. Like BMI, De Vrij has been capped at the U-21 level and senior level for the Netherlands.
He captained Feyenoord in the 2012-13 season and was a pivotal cog in a defense that conceded the third-fewest goals in the Eredivisie.
He made his Feyenoord debut when he was just 17 years old and has gone on to play in 103 league matches since 2009.
Standing at 6'2", De Vrij can compete in the air and is a fantastic tackler. He's a quick player with good positional sense who's comfortable with the ball at his feet, stemming from his time as a central midfielder.
He's consistently improved with each passing season and is one of the brightest Dutch defensive prospects in recent memory.
One concern about De Vrij is that he's had nagging ankle injuries, but Milan's medical staff, known for extending the careers of aging veterans, would hopefully be able to address the root of the problem.
At this point in his career, he looks to be a more polished prospect than Martins Indi. His contract runs until 2015 and will likely cost around €10 million, should Milan make an approach. Like with the Martins Indi proposal, Urby Emanuelson could be thrown into the deal to lower the cash portion.
There haven't been any concrete reports linking De Vrij to Milan, and considering they've been tracking his teammate, Milan's scouts will have surely seen a good bit of the Dutch defender. This possibly alludes to the scouts preferring BMI over De Vrij.
If Milan are to sign a Feyenoord defender, it seems like Bruno Martins Indi will be the man, but Milan's vice president and resident transfer market guru, Adriano Galliani, shouldn't overlook De Vrij, who looks primed for a long, successful career.
Real Sociedad were much the surprise team of La Liga last season, after they finished in fourth place with the possibility of qualifying for the UEFA Champions League.
Sociedad leaned on their very gifted attackers, including Carlos Vela and Antoine Griezmann, but just as crucial to their success was their defense, which conceded the fourth-fewest goals in La Liga last season.
Right-back Carlos Martinez was the standout performer of their defense, but not far behind was 22-year-old centre-back Inigo Martinez.
Martinez came up through the youth system at Real Sociedad and has made 60 appearances for his side since 2011, including 34 starts last term.
In those 60 matches, Martinez has scored seven goals, making him the most prolific scorer on this list, including these two strikes where he caught the goalkeeper out of position.
He's the shortest player of the four at just under 6'0", but quite ironically is perhaps the best in terms of aerial ability. He's a left-footed defender that reads the game quite well, capable of starting an attack from the back with his penchant for playing a long ball.
He starred for the Spanish U-21 side that recently took home the trophy at the 2013 UEFA U-21 European Championships and looks to be the future at centre-back for the Spanish national team.
The only player on this list not to have earned a senior international cap, Martinez emerged as a transfer target of Spanish giants Barcelona and Real Madrid earlier this summer, according to Oscar Badallo at Marca (article in Spanish).
Barcelona seem to be more keen on either Thiago Silva or David Luiz, while Real Madrid have Pepe, Sergio Ramos, Raphael Varane and Raul Albiol, who will all be ahead of Martinez on the depth chart.
With a similar playing style to Carles Puyol, Martinez has a huge release clause in his contract and considering Spain's top players tend to stay in their home country, it will be incredibly difficult for Milan to actually be able to sign the player.
This one is the most improbable, yet being one of the brightest centre-back prospects in world football, he deserved a mention.
With Barcelona focused on other players and Real Madrid's crowded defensive corps, it could open the door for another top European club to swoop for Martinez, so why not Milan?