Diego Costa's dispute with Chelsea is no closer to being resolved after it emerged that his case is now the subject of legal action.

Costa is not a part of Chelsea's first team squad heading into the new season and is still working on his match fitness on his own back in Brazil.

The Spain striker claimed he was informed by coach Antonio Conte via text message in June that he was not a part of the club's plans anymore.

However, Conte claims that Costa and his agent Jorge Mendes were told in January that the forward would be sold in the summer.

The Spain striker, who wants a transfer back to Atletico Madrid, has instructed his lawyer Ricardo Cardoso to get involved.

The 14 senior Chelsea players available to Antonio Conte 15 show all The 14 senior Chelsea players available to Antonio Conte 1/15 Antonio Conte has put pressure on the Chelsea board to strengthen further with just 14 senior players available AFP/Getty Images 2/15 Willy Caballero REUTERS 3/15 Antonio Rudiger Arsenal FC via Getty Images 4/15 Marcos Alonso Getty Images 5/15 Cesc Fabregas Getty Images 6/15 Andreas Christensen Alexander Hassenstein/Bongarts/Getty Images 7/15 N'Golo Kante AFP/Getty Images 8/15 Victor Moses AFP/Getty Images 9/15 Alvaro Morata AFP/Getty Images 10/15 Pedro Getty Images 11/15 Willian Getty Images 12/15 Michy Batshuayi EPA 13/15 Gary Cahill Bongarts/Getty Images 14/15 Cesar Azpilicueta AFP/Getty Images 15/15 David Luiz AFP/Getty Images 1/15 Antonio Conte has put pressure on the Chelsea board to strengthen further with just 14 senior players available AFP/Getty Images 2/15 Willy Caballero REUTERS 3/15 Antonio Rudiger Arsenal FC via Getty Images 4/15 Marcos Alonso Getty Images 5/15 Cesc Fabregas Getty Images 6/15 Andreas Christensen Alexander Hassenstein/Bongarts/Getty Images 7/15 N'Golo Kante AFP/Getty Images 8/15 Victor Moses AFP/Getty Images 9/15 Alvaro Morata AFP/Getty Images 10/15 Pedro Getty Images 11/15 Willian Getty Images 12/15 Michy Batshuayi EPA 13/15 Gary Cahill Bongarts/Getty Images 14/15 Cesar Azpilicueta AFP/Getty Images 15/15 David Luiz AFP/Getty Images

Last week, Cardoso said Costa was bringing a claim against Chelsea to force a move to Atletico.

He said: "We are going to activate all the legal mechanisms [to secure Costa's exit] and formally present a transfer request.

"When he was already with the Spain national team [for a friendly against Colombia last June] and before travelling to Brazil to enjoy his holidays, he was released from Chelsea by SMS by the coach Antonio Conte.

"Obviously, this release, in the way it was done, and how it became known by everyone, was unfair treatment and a lack of respect to the player on the part of Conte which is unacceptable and inexcusable.

"Chelsea have not just not denied nor corrected the coach, either in public or private, but instead renewed his contract. This shows that they knew about and were in agreement with the release of Diego Costa and the way it was done.

"Such discriminatory behaviour makes it impossible for Costa to return to Chelsea while Antonio Conte is coach.

"There is no way that he can continue to play for Chelsea, a message which has been communicated various times to those in charge there.

"And he will not play for any other club which is not Atletico Madrid, a club where he had sporting success, but above all where he was always respected, even after he had joined Chelsea."

Cardoso's comments were dismissed by the club, with spokesman Steve Atkins saying last Friday: "The premise the lawyer has put forward is just wrong.

"The decision on Diego was made back in January. The player knew the decision, his agent knew the decision, clearly the lawyer has not been well informed.

"The lawyer's argument that Antonio as a coach has forced the player out by text message in June is just nonsense. We'll just have to see what the window brings."

Now that the matter has become a legal issue, Conte did not answer questions about Costa in his pre-match press conference ahead of the Burnley game. He and the club will continue to maintain their silence on the issue until it is resolved.

Chelsea want £50m for Costa but Atletico, who are banned by Fifa from registering any new players until January, have offered just £26m so far.

AC Milan did hold talks with Mendes earlier this month over a transfer, but made it clear they were only interested in a permanent deal, rather than a short term loan.

The Italian club thought negotiations had gone well only for Costa's lawyer to reveal that his client was taking a stand against Chelsea to force a return to Atletico.

Costa has scored 52 League goals for Chelsea since joining from the La Liga club for £32m in 2014, helping them win the League in 2015 and 2017.