The Blues signed the Spain international from Atletico in summer 2014, after he fired them to a La Liga title and the 2014 Champions League final where they faced fierce rivals Real Madrid.
The 27-year-old has since notched up 32 goals in 54 Premier League appearances for the west Londoners and was an integral part of the squad that lifted the English title during the 2014/15 campaign.
But Costa has often been linked with a return to his former club and Mirror Football reported earlier this week that Atletico had opened talks with Chelsea regarding a potential summer move.
And The Daily Star now claim that the Brazil-born striker has informed the Blues he wants to leave this summer, whilst Diego Simeone’s side have tabled a formal £40million offer.
Manager Antonio Conte is reportedly ready to sign off on Costa’s departure and further talks between the two clubs are expected next week.