It has been suggested Lookman is trying to force a move to RB Leipzig, where he enjoyed a loan spell last season.
“Lookman knows very well why he wasn't in the squad last week," said Silva. “It was a technical decision and he knows very well why. But I can tell you he has trained very well this week and responded how I wanted him to.
“Even if he's not really happy he has to be in the future and it is a matter of him fighting for what he wants in his career.
“In this moment he is our player, I am happy to keep him as our player, and now it is up to him to fight for his position, for a place in the starting XI and in our squad list as well."