Chelsea has been left searching far and wide for the player it has been unable to replace.
Diego Costa: one of the more controversial players Chelsea have had in recent times, but a talented one none the less.
He scored crucial goals and did stupid things during his eventful time at Stamford Bridge, but do Chelsea miss the fiery forward now?
Chelsea fans were left perplexed with Antonio Conte's insistence to get rid of a player who had done so much for the club last summer. After signing for the blues in the summer of 2014, Costa went on to become somewhat of a legend.
He scored an impressive 58 goals in 120 appearances for The Blues and was a crucial part of a team that won two league titles and a League Cup in the space of three seasons. However, Conte clearly did not feel the love for Costa that many of the fans did, and told him via text message that he was no longer wanted at the club.
It was a sad way for his time at Chelsea to end, and Costa told ESPN Brasil that Chelsea treated him like a 'criminal.'
The news that they would be losing their top scorer did not originally go down well with fans of the London club, but many minds were changed when the club forked out £58m for Real Madrid striker Alvaro Morata.
Costa's international teammate had always scored goals, despite never being the main man at a club. He came in with a reputation of being a clinical finisher and it initially looked like Chelsea had bagged themselves a superb striker. He scored six goals in his first five league games, but his form has dipped since then, only adding four more to that tally.
This has lead to questions being asked of the 25-year-old's ability, and has caused Chelsea fans to grow increasingly frustrated, with Morata not scoring since Boxing Day and the club's form subsequently faltering.
People are now wondering if Chelsea would have been better off keeping Costa because despite his occasional attitude problems, he could always be relied upon to score goals. Morata has also shown he may have a short fuse, getting sent off for dissent in the recent victory over Norwich.
It isn't just the fans who are becoming frustrated. Chelsea are being linked with a whole list of big front men, such as Andy Carroll and Peter Crouch. This suggests the board feel the team miss the influence of a striker who will really 'put himself about'.
Since rejoining Atletico, Costa has shown his former club what they are missing. He has grabbed three goals in four games, and this will surely rub salt in the wounds of Chelsea fans.
Many will say that Morata is a safer option for Chelsea in terms of Costa's reputation for being a liability in terms of his discipline. This is a superficial view, because in three seasons of English football, the former Chelsea man only received one red card, a number already matched by his successor.
The debate on whether the club sitting third in the table miss Costa is dividing opinion among fans, with many drawing comparisons between the pair.
It is unfair to make a judgment on Morata just yet, and every striker goes through bad patches. He is still just 25-years-old and is on course to equal or beat the goal contributions made by his predecessor in his best season for Chelsea.
The team definitely miss parts of Costa's game, and it is still yet to be seen if Morata can help fans forget all about Diego.