Atletico Madrid have advised Diego Costa to return to Chelsea with the Blues threatening to sue the forward for up to £50m.
The Daily Mail have reported that the Spanish club have told Costa to end his exile in Brazil and attempt to push through a January move after this summer's failed attempt.
The 28-year-old has refused to return to the Blues' Cobham training ground having been informed by manager Antonio Conte that he is not in his plans for this season.
He revealed his intention to return to Atletico but the move failed to materialise due to Chelsea's £50m demands.
But the Express have now reported that the Premier League champions could take Costa to court if he continues to avoid returning to the club.
They could reportedly sue up to £50m and claim breach of his £185,000 per week contract, which still has two years remaining.
Costa is now believed to be consulting with his lawyers, while Chelsea claim that he must return to fulfil his contractual obligations.
But the Spain international has made clear his belief that his contract became irrelevant when Conte told him via text that he would no longer play for the club.
Costa claimed earlier this month in an interview with the Daily Mail that he had been treated like a "criminal" by Chelsea.
“I am waiting for Chelsea to set me free," he said. "Why won’t they let me go if they don’t want me?
“My desire is to go to Atletico (where he played from 2010-14). I’ve spoken to Chelsea director Marina Granovskaia. I said, ‘If the manager doesn’t want me, I want to go to Atletico Madrid’.
“They want me to be there training with the reserves. I wouldn’t be allowed access to the first-team dressing room and I would have no contact at all with the guys. I’m not a criminal! I don’t think it is fair after all I have done to be treated like that.”