The Italian was asked about including the all action midfielder in his Conference League squad.
With several senior players missing from that group, the youngster could get more chances to play in the group stages.
Maresca told reporters: "I said already to him personally, and to you in the press conference: I really, really like Carney. The problem is that we have so many attacking midfielders that he is going to struggle to find space.
“Because of his past, in terms of injuries, the best thing to do was to go and prove himself that he is fit and can play 30 or 35 games and then come back here.
"Unfortunately we didn't find any solutions and now he is one of the players in our squad and we can use him."
He then added on Ben Chilwell: "Ben is now probably the only one that is still here. We are going to sit with him and find a solution because he is the only one. He is probably going to be back with us in a training session, we will see, because right now he is not training with us."
On whether he will let Chilwell back into the group, he finished: "The reason why he is training apart is because the idea was for him to leave but because he didn't find a solution, he is probably going to start to train with us. In the moment, if we decide that, he is going to be one of the players."