LONDON -- Diego Costa and Chelsea are engaged in legal proceedings as the acrimonious battle to resolve the unsettled striker's future drags on, sources have confirmed to ESPN FC.
Chelsea begin their Premier League title defence against Burnley at Stamford Bridge on Saturday without their top scorer last season, who has remained in his home town of Lagarto in Brazil while talks continue over a move back to Atletico Madrid.
Last week, Costa's lawyer Ricardo Cardoso threatened to utilise "all possible legal mechanisms" against Chelsea and submit a formal transfer request in response to what he referred to as the "discriminatory behaviour" of head coach Antonio Conte towards his client, who was informed by text earlier this summer that his career at Stamford Bridge was over.
Chelsea's position is that Costa and his representatives were made aware in January that he would not be in Conte's plans for this season, and a club spokesman later described Cardoso's allegations against the Blues head coach as "nonsense."
But sources with knowledge of the situation have confirmed that the dispute is now a legal matter, though details of the proceedings have not been disclosed.
There is no timeframe for Costa to return to England and the expectation remains that he will be sold to Atletico in the final three weeks of the transfer window, though the Spanish club remain some way off meeting Chelsea's valuation of the 28-year-old.
Costa's absence, coupled with injuries to Eden Hazard and Pedro Rodriguez, means that Conte is likely to pick both Michy Batshuayi and club-record signing Alvaro Morata in his starting XI against Burnley.
"I think this is a great possibility for Michy," Conte said in a press conference on Friday. "He's playing every game from the start [in preseason] and it's very important for him to play well. Michy is working well and putting in 120 percent in every moment, during training sessions and in the games.
"We're talking about a young player and he needs to develop, but for sure he's trying to put his best in every moment.
"We worked very hard with him last season. He didn't play a lot but I think he adapted himself well in our style of football. He has a lot of space to improve -- he's a young player and he needs to work."
Chelsea head into the new season with a squad noticeably short on numbers thanks to several key injuries and difficulties in the transfer market, but Conte insisted that there can be no excuses for his team when the football begins.
Asked if the real Chelsea won't be seen until Hazard and summer signing Tiemoue Bakayoko return to fitness, Conte replied: "I hope to see the real Chelsea tomorrow, because now the season is starting and we must be ready, [even] if in this moment many players are missing.
"We have to go with these players, we have to try to play good football, try to win the game. For sure it will not be easy in this part of the season, but I don't want to find any excuse for me, for my staff or for my players. It's not important who is injured. It's important to try and do our best."