Diego Costa's lawyer Ricardo Cardoso has confirmed the striker will hand in a formal transfer request at Chelsea.
Costa has been told he is not part of Antonio Conte's plans for the upcoming season and the Spain international is now widely expected to leave following the arrival of compatriot Alvaro Morata from Real Madrid.
Costa's lawyer Cardoso told Spanish news agency EFE that the forward intends to 'formally request a transfer' away from Stamford Bridge.
"We are going to use all legal mechanisms to hold Chelsea accountable for this behaviour, making it possible for Diego Costa to leave," Cardoso said.
Sources close to the player have told Sky Sports News that Atletico Madrid remain the most likely destination for Costa, although nothing is agreed.
Costa spent four seasons with the Spanish club before leaving to join Chelsea in a £32m transfer in 2014.
Atletico Madrid are currently banned from signing new players until the start of next year, prompting suggestions Costa could join AC Milan on loan until January.