Diego Costa returns to Chelsea

From Chelsea’s point of view, they did not want to allow Costa to force his way out of Stamford Bridge for fear of setting a precedent.

CHELSEA and Diego Costa’s reconciliation could be about to be begin, with the striker having returned to London after nearly three months in Brazil.
The main reason for his refusal to return to the United Kingdom was the fact that Antonio Conte told him he is not needed for the 2017/18 season and that the Italian ordered him to train with the reserves.
However, it appears that the 28-year-old has finally agreed to accept the Blues’ wishes and to recover his fitness with their reserves, at the same time as negotiations continue to finalise a January return to Atletico Madrid.
From Chelsea’s point of view, they did not want to allow him to force his way out of Stamford Bridge for fear of setting a precedent, and director Marina Granovskaia was not willing to push on with negotiations until the Spain international came back.
Given that ultimatum, Atletico were also keen for Costa to resolve his differences with his current club and he received calls from Andrea Berta, Diego Simeone, Tiago and Filipe Luis.
Now that he has returned, developments are expected in the coming weeks, with respect to a January transfer to the Spanish capital.
If he does then move, there will be a need for an intense training plan, given that he hasn’t had any supervised workouts this summer, but the fact that he is back in London and that he’d been left out of Chelsea’s Champions League squad means there could be some light at the end of this very long tunnel.
―marca.com