The Spain global made it clear he favoured a return to Atletico Madrid and has been holding out for such a move ever since and according to Goal.com, with no deal coming his way Chelsea have taken the decision to include Costa within their squad. The Spain forward is insistent that Chelsea are in the wrong and that Conte destroyed their relationship when the manager sent a blunt text message to inform him that he would not figure in his plans for this season.
Costa's registration offers the possibility of a shock lifeline but, more realistically, it is the latest move by Chelsea in a possible legal battle.
Atletico are under a transfer embargo until January and so Costa would be unable to play for Diego Simeone's team until the turn of the year.
The same report claims that Conte wanted a total of eight new signings over the summer and was keen to see the west London side secure deals for Van Dijk, Sandro and Lukaku. But the Blues insist it was decided in January, with the striker and his agent, Jorge Mendes, that Costa could leave this summer.
It was unclear whether Costa would be named in the club's Champions League squad, which was due to be announced at 11pm last night.
"But if Atletico and Chelsea don't come to an agreement and Atletico don't make a big effort, I can't keep on wanting to play for a club that isn't going to make a bigger effort to try and sign me".
Costa, 28, is in his hometown of Lagarto in Brazil and is being fined £300,000 for every fortnight of his absence. "As the main striker I always have to be a target for my team-mates".
The first is that he return to England, the second that he return to training, the third that he get himself match fit and the fourth that he make himself available for selection.
This four-point demand puts the club on a collision course with Conte.
Courtois got the ball rolling by posting a picture to social media of him celebrating Chelsea's Premier League title triumph with Costa.