Antonio Conte has admitted that he cannot yet guarantee Diego Costa will remain a Chelsea player beyond the end of the transfer window, amid talk of a return to former side Atletico Madrid.

Atleti are said to be "confident" of landing the Brazilian-born Spain international this summer, just two years after he departed the Vicente Calderon to join the Blues.

Costa was once again left out of Chelsea's squad for the 3-2 defeat against Real Madrid on Saturday evening with a back injury, although he could feature against AC Milan on Thursday should he still remain at the club.

"I can say that today Costa is a Chelsea player," Conte is quoted as saying by Sky Sports News. "He didn't play in these games because of injury and if he solves the injury and I see in training that he is in good shape it can be possible to see him in the next game against Milan.

"But I can say only this. I speak only for today and today Costa is Chelsea's player. Tomorrow if you ask me if Costa will remain with us, I don't know."

Conte would not be drawn on speculation over rumoured target Romelu Lukaku, meanwhile, adding: "I do not want to speak about the players of other teams. This is not respectful to the club or to their players. I prefer not to speak.

"The transfer market is not the most important thing. The important thing is to build a team - a team that plays in good and bad situations and concentrates and works together."

Costa scored 16 goals for Chelsea last season as they finished 10th in the Premier League.