Premier League sides Arsenal, Tottenham and Wolves are all reportedly interested in the France winger.
Lemar has made 21 appearances for the LaLiga side this campaign but has made just 10 starts.
"The facts speak for themselves, better than words. It is certain that he has not been able to show all his qualities," Simeone said.
"Each time that he has been available, I have tried to play him. I have always been enthusiastic about his qualities as a player.
"He has not met the expectations set for him, but we have always had the same expectations.
"Today, who is to know if he will stay or not. His representatives are working hard. The clubs, they operate on what they need."