Diego Costa is reportedly planning to hand in a formal transfer request in order to accelerate his move away from Chelsea.
In June it emerged that the 28-year-old had been informed by Blues boss Antonio Conte that he would not be part of his plans going forward and was free to find a new club.
The Spain international is keen on a return to Atletico Madrid but is unable to move to the Spanish capital until January, when Atletico's transfer embargo is lifted.
Costa's agent Jorge Mendes has been looking for a stopgap solution, including a potential six-month loan to AC Milan, but Costa now intends to speed up the process and make Chelsea "accountable" for ostracising him.
The striker's lawyer, Ricardo Cardoso, confirmed that his client would submit a formal transfer request, adding: "We are going to use all legal mechanisms to hold Chelsea accountable for this behaviour, making it possible for Diego Costa to leave."
Costa joined Chelsea from Atletico in 2014 and has since gone on to score 52 goals in 89 Premier League appearances.
