Diego Costa left out of Chelsea's Champions League squad

Diego Costa has been left out of Chelsea's squad for the Champions League group stage as the dispute over his future rumbles on.

Speculation that Costa -- who remains in his home town of Lagarto in Brazil -- could yet be brought back into the fold at Stamford Bridge was sparked by his inclusion in Chelsea's submitted Premier League squad list earlier this week.

Chelsea subsequently failed to agree a deal to sell Costa to Atletico Madrid before Friday's transfer deadline in Spain, but the fact that his name has been omitted from the Champions League list underlines the fact that the Premier League champions are keeping the option of a January sale open.

If Costa were to represent Chelsea in the Champions League group stage -- where they have been drawn alongside Atletico -- he would become ineligible to represent the Spanish club in the competition for the rest of this season, further lowering his potential sale value.

Chelsea have instructed Costa to return to England, return to training, get himself back to full fitness and put himself in position for first-team selection, though it appears highly unlikely that head coach Antonio Conte would consider picking him again.

Costa accused Chelsea of treating him "like a criminal" and Conte of "lacking charisma" earlier this summer after the former Italy boss sent a text message confirming that the striker would not be wanted at Stamford Bridge this season. 

Chelsea insist that Costa and his representatives knew his time at the club was coming to an end as far back as January, when he was briefly dropped from the squad by Conte following a training-ground row and a lucrative offer from Chinese Super League club Tianjin Quanjian. 

Costa remains adamant that he will not return to England until Chelsea agree to sell him to Atletico, who were unable to register new players this summer due to a FIFA-imposed transfer ban.

Last month, he told ESPN Brasil that he believed Chelsea were pricing him out of his desired move with an unrealistic valuation. 

Liam is ESPN FC's Chelsea correspondent. Follow him on Twitter: @Liam_Twomey.