The reason he is apparently leaving? Jose Mourinho keeps leaving him on the bench, even though he is the best player in the Chelsea squad.
Except, this season, he isn't.
It is not for no reason that Mata was voted as the Chelsea fans' Player of the Year for two years running. In 2011 he became the first signing of the transition era at Stamford Bridge, as the owner looked to transform his team of tough title winners into tiki-taka masters.
The flair Mata exhibited in his debut season reminded many fans of Gianfranco Zola, a player who is still universally adored at Chelsea. They took him to their hearts and he responded in kind, picking up a Champions League winner’s medal for his troubles.
He was joined by two of the players who are keeping him out of the side at the moment, Eden Hazard and Oscar, and the trio formed a formidable partnership that was one of the only stable good points in a season that left a bitter taste in many fans' mouths.
Mata was better than his other amigos last season. The team looked flat without him and he made 64 appearances as he carried them to another European title.
This is all great, right? A player who has achieved all of these amazing things and made such a positive impression over just two full seasons should be starting every game.
Except, professional athlete or not, Mata is tired. His pace has dropped, as has his decision-making, and although his limited game time may have had some effect on this, it is not the only reason.
Mata has played in some kind of international tournament every summer since 2009. The sheer number of games he featured in for the Blues last season meant that he arrived at the Confederations Cup exhausted, yet still appeared in the final, which Spain lost to hosts Brazil.
He may have missed Chelsea's tour of Asia so that he could have a proper rest, but that didn't quite cut it.
The form of his fellow attacking midfielders must also be taken into account. Oscar has been exceptional as an all-round No. 10, even though the signs indicate that he will evolve into a deeper-lying playmaker. Hazard has been nothing short of phenomenal, while new signing Willian has worked his socks off to prove himself and certainly deserves his place in the starting XI.
Which leaves Mata on the bench at Chelsea—for now.
The popular narrative is that his future at Stamford Bridge hinges on whether or not he makes the Spain squad for the World Cup. If he does, he'll be fourth choice at best. However, if he is not selected, it could be a blessing in disguise.
Mata has a winner’s medal from 2010 and the opportunity to rest properly could improve his chances to get ahead of Cesc Fabregas, David Silva and Jesus Navas for Euro 2016 and beyond. Also, the opportunity to work with Mourinho for a full preseason would allow him to improve the areas of his game that currently need work.
If Mata did leave Chelsea, it would be a very sad day for the supporters, but there is no solid indication that he will.