Diego Costa will not play again for Chelsea and will only join Atletico Madrid, according to the Spain international's lawyer Ricardo Cardoso, who says his client is to formally submit a transfer request to the Premier League club.
Costa, 28, joined Chelsea from Atletico for €38 million in 2015, and has won two Premier League titles during his time in London.
However, a falling-out with Antonio Conte over the course of the 2016-17 season led the Chelsea boss to inform Costa by text message in June that he was no longer required at the club.
Speaking to news agency EFE, Cardoso said that Conte and Chelsea were to blame for the situation and the only acceptable resolution was for them to now allow him to rejoin Atletico.
"We are going to activate all the legal mechanisms [to secure Costa's exit] and formally present a transfer request," the lawyer said. "In three seasons at Chelsea he won two championships, and was the decisive player in those victories.
"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."
Conte said last month that he had made clear to Costa in January that he would be allowed to leave this summer.
Costa's current Chelsea contract runs until 2017 and he was linked with a €90m move to the Chinese Super League, having almost moved to Asia in January, though Atletico are unlikely to pay anything close to that fee.
Atletico are known to be keen to re-sign a player who won the 2013 Copa del Rey and 2014 La Liga title during his time at the club, but the situation is complicated by a FIFA transfer ban that means they cannot register new players until January 2017.
While both the Chelsea and Atletico squads have returned to preseason training in recent weeks, Costa has remained on holiday at home in Lagarto, Brazil, regularly drawing attention by antics recorded on social media, which have included partying in a Rojiblanco shirt and appearing to joke about his broken relationship with Conte.