He is going to Chelski, I think the agreement was reached a couple of weeks ago, judging by the noise about Costa going to China re-surfacing about that time. He wants Champs League, is a Chelsea fan and he fits their style of play under Conte.
It might also account for the team playing with less intensity knowing that he is off, that and the fact we cant get 5/6 and cant be caught for 7th.