“He is a young player who is a fantastic talent and we will try to work with him in a positive way and to make him feel part of the team,” Mancino said.
“It’s a very difficult moment for him, but he will be back and will continue to do so.”
Mancinos comment comes as Chelsea’s transfer window closes on Thursday with the club unable to make any signings for next season.
Mancinos comments come a day after Costa, the subject of intense speculation over the past few weeks, revealed he would be returning to Stamford, despite being under contract with the Blues until 2020.
Costa, who scored 15 goals in 36 appearances for Chelsea this season, was also linked with a move to Bayern Munich and Tottenham Hotspur, who he is understood to have been a target for during the transfer window.
The 25-year-old said at the weekend that he would not return to Chelsea next season after failing his medical.
Costa’s agent, Mino Raiola, has also said the striker would not be joining the Premier League champions in the summer.