1) He might come back to haunt Mourinho
Now Mourinho can control whether Mata stays or not but he might not have as much say in where he wants to go. United can refuse to sell him to a rival but if it becomes absolutely impossible to deny a huge offer.
Last time Jose was wise enough to sell Mata after Chelsea had already faced Manchester United twice in the league, so it did not directly affect them. If Mata is sold in the summer and he invariably joins a rival then it becomes a problem for Mourinho.
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There are some rumours swirling around that Juan will join Everton who are under new ownership and are aiming to break into the top four. He might be the instigator for them and really help them push for a place in the Champions league.
But he is still a Manchester United player and Mourinho might just find a way to incorporate him in his system but it doesn't look very likely after the first warm up game that he’ll be sticking around for too long.
