The January transfer window has never been the ideal time to do business in football.
Clubs put ridiculous prices on their best players and half of them are cup-tied for all of the major competitions. Anybody who is transfer listed during the winter window has either fallen out with the manager or the fans or the owner and, more often than not, they are failing to perform to their potential.
Still, needs must and there are occasions where transfer business conducted in January can pay dividends. Let's take a look at the best, and worst, January transfer window signings that Chelsea have made.
The best players will have made a major positive impact on the club or have increased their transfer value. The worst have not done enough to justify their transfer fee or were unnecessary additions to the squad.
Transfer fees are from transfermarkt.co.uk unless otherwise stated. Statistics are from ESPN stats.
Chelsea hit the panic button when they paid £7 million for Ba in January 2013.
Although the Senegalese striker had been scoring for fun at Newcastle United, the fact that he had failed medicals at Stoke City and West Ham should have stamped a great big "stay away" sign all over him.
With a good run of games, he could certainly score a decent amount of goals, but his dodgy knees will prevent him from becoming the world-class finisher that Chelsea need.
David Luiz joined Chelsea in January 2011 from Benfica. The Brazilian centre-half had become a cult hero in Portugal, despite making some silly errors, and he set about doing the same on his arrival in London.
In his full Premier League debut against Fulham, Luiz was named man of the match, despite conceding a penalty in the dying minutes of the game.
Luiz is a rare breed of footballer who understands how lucky he is to be doing something he so clearly loves for a very comfortable living. He turned down interest from Barcelona in the summer and is widely tipped to be the next club captain.
Ricardo Quaresma joined Chelsea on loan from Inter Milan in January 2009.
The 25-year-old was struggling to fit into Jose Mourinho’s plans at the San Siro and it was felt that a good run of first-team football in a competitive league would help him return to form.
At the time, Chelsea were in dire need of a winger and it seemed like Quaresma could solve that problem until the end of the season. However, he only made five appearances for the first team before being consigned to the reserves for the remainder of his loan.
Chelsea signed Branislav Ivanovic from Lokomotiv Moscow in January 2008 for a fee believed to be around £9 million.
The Serbian defender has since become a key player for the Blues, making his mark at both ends of the pitch. His strength in the air has seen him score 23 goals for the club, while his presence in the back line is enough to put off plenty of attackers.
Chelsea signed the 18-year-old Franco Di Santo for a fee of around £3 million in January 2008.
The youngster made an instant impact in the reserve side before being given his chance in the first team the following year.
Despite some impressive performances in the FA Cup in particular, Di Santo was loaned out to Blackburn Rovers for the Blues’ double-winning season before being sold to Wigan Athletic for £2 million in the summer of 2010.
Chelsea signed Belgian starlet Kevin De Bruyne from Racing Genk in January 2012. He was taken on the 2012-13 preseason tour of the USA before being loaned out to Werder Bremen for the full season.
He made a huge impact in the Bundesliga, scoring 10 goals in 32 appearances, and attracted interest from plenty of clubs.
He was recalled to Chelsea for the 2013-14 season but has failed to break into the first-team on a regular basis. Rumours persist that he is heading back to the Bundesliga on a permanent basis and there are plenty of Blues supporters who would be sad to see the 22-year-old leave.
Ben Sahar joined Chelsea at the age of 16 for a fee of £320,000. He made a handful of appearances in his first season at the club but failed to make an impact.
The Israeli international was then loaned out to QPR, Sheffield Wednesday, Portsmouth and Eredivisie side De Graafschap before being released by Chelsea in 2009. He has since moved to Bundesliga side Hertha BSC.
Nicolas "Le Sulk" Anelka once had the highest accumulated transfer fee of any professional football player.
When he moved to Chelsea from Bolton in 2008 for a fee of £15 million, it was primarily to provide back-up to Didier Drogba.
He lived up to his nickname in the Champions League final that May by refusing to take the fifth penalty in the shootout and ended up missing in sudden death to break blue hearts around the world.
However, he went on to establish himself as a useful squad player while Drogba was injured and scored 59 goals in 184 appearances for Chelsea.
Chelsea re-signed peter Osgood from American side Philadelphia Fury in January 1979.
The King of Stamford Bridge came home to save the club from relegation but was unable to make the impact that his legend promised. He left at the end of the season with his legend intact.
Scott Parker has played for five London clubs including his current employers, Fulham. He began his career at Charlton Athletic before moving to Chelsea in January 2004.
Parker scored his only goal for the club against Portsmouth before new signings and injuries limited his chances. Parker ended up leaving for Newcastle in the summer of 2005 for a loss of £3.5 million.
When Gary Cahill was brought in as a defensive reinforcement in January 2012, there were a few Chelsea fans questioning the rationale behind this move.
The Blues certainly needed a centre-half, but with the inflated prices in January and the limited availability, bringing in a player from relegation candidates Bolton Wanderers seemed like folly.
However, Cahill made good on his ambition to win trophies within a few months of joining the club. While he is not yet at the same level as the legendary John Terry, he could turn out to be among the Blues’ best January buys.
It took him three months to score his first goal for the Blues and he has obviously felt the pressure of the price tag.
His performances for Chelsea have ranged from the sublime—against Barcelona at Camp Nou in 2012 and Bayern Munich in the 2013 Super Cup—to the ridiculous, which are too numerous to mention.
There is still hope that he could recapture the form that saw him command such a huge fee, but as it stands now, he must go down as Chelsea’s worst January panic buy.