Appearances: 39 starts (+2 as substitute).
Minutes: 2378 in Premier League; 330 in domestic cups; 663 in Champions League.
Statistics (per 90 minutes, Premier League): 0.45 goals scored (no penalties), 0.23 assists, 2.58 shots (1.37 on target).
Diego Costa's first season with Chelsea was a major success. Scoring a goal on his Premier League debut against Burnley in August 2014, Costa went on to add 19 more in the league and another one in the League Cup final win over Tottenham Hotspur. His suspensions and hamstring issues, carried over from his Atlético days, limited him to just 26 league games, but he was undoubtedly one of the key pieces in our double-winning campaign.
Costa's second season with Chelsea didn't start off nearly as well however. Another hamstring injury kept him out of our Community Shield match against Arsenal, but he recovered in time to return for the season opener. After two scoreless games, he opened his account in Chelsea's first win of the season, (3-2 away at the Hawthorns), but he would score just three more times in the next 19 games, and only against the likes of Maccabi Tel Aviv, Aston Villa and Norwich City. In the meantime he was also suspended for three games due to his clash with Arsenal defenders Laurent Koscielny and Gabriel in our 2-0 win over the Gunners in September.
Chelsea's poor record in the league lead to manager José Mourinho's sacking in December. Guus Hiddink was called on to return to the club for a second spell as interim boss. That change (or was it the infamous "3 rats" banner?) inexplicably sparked Costa back into in form. He scored a brace in Hiddink's first game in charge and then hit the back of the net in 9 of his next 14 games. All-in-all, Costa finished with a decent 16 goals across all competitions, though his season ended on a down note as he picked up a sixth hamstring injury since 2014. This one has forced him to miss Euro 2016 with Spain as well.
While Costa isn't known for being the most technically gifted striker nor one with the greatest physical tools, he's still one of the most complete goalscorers in the game. Perhaps his secret lies in his mental fortitude; and that includes his on-pitch antics and every little action he takes to get into his opponents' heads while walking a fine line in terms of in-match punishments (he's not been so lucky to escape post-match punishment however). Unfortunately, his reputation, however unjustified or justified, has preceded him both in terms of treatment by the #CostaCrimes media and in terms of refereeing decisions.
The Good: Costa's brace in our game against Watford. A great gift to Guus Hiddink on his return to Chelsea as interim manager.
The Bad: His cameo as a half-time substitute in our first match against Bournemouth this season, a 1-0 loss at Stamford Bridge. Not an impressive showing from the striker who only recorded 1 shot - albeit on target - and picked up a yellow card in 45 minutes of play as the Chelsea season went from bad to worse.
The Ugly: His first ever red card for Chelsea, after picking up two yellow cards in the FA Cup match against Everton. Costa only recorded 1 shot - this time off target - through 83 minutes of playing time, and picked up an early yellow card. An altercation with Gareth Barry ultimately led to his second one, and an early bath in the dressing room coupled with his second suspension of the season.
Verdict: The Gonzalo Higuaín and Romelu Lukaku rumours hover around Stamford Bridge, with the latter especially picking up more steam lately. But this shouldn't necessarily be a reason to worry about Costa's future, since bringing in a new striker doesn't have to mean excluding another from the picture - especially with Antonio Conte's potential for new ideas set to arrive this summer.
Costa has proven himself as a lone centre forward at Chelsea but he also got to be a second striker in his Atlético Madrid days, feeding off Radamel Falcao as the Colombian poacher made his case to be one of the best players in the sport. While the addition of Higuaín or Lukaku wouldn't guarantee a change in our tactical system from the get-go, Costa's versatile enough to fit into a different system then the popular 4-2-3-1 modern standard.
That said, striker isn't a "position of need" for Chelsea at the moment, and that is largely due to Costa's goals over the past two seasons. A welcome change of pace after several seasons to Fernando Torres & Co. While Costa's hamstring issues remain a concern, his form in the second half of the season should be proof enough that he hasn't completely forgotten how to be the Diego Costa of our title-winning season and that should bode well for the future.