The Morocco international pulled up at Selhurst Park on Tuesday and had to be replaced early in the first-half.
“It is a little bit questionable at the minute,” Glasner said in his pre-match press conference. “It looked really bad, and the next day he was very stiff in his knee.
“But the examinations were not so bad, but also not clear enough by the next day, so we have to wait now for the next two weeks to see if the knee is swollen to get the right diagnosis for the future.
“It doesn’t look so serious, we will miss him definitely for several weeks, but what it looked like is that the ACL is not ruptured, which is very important.
“We’ll see within the next two weeks.”
Palace take on Chelsea at Stamford Bridge on Sunday, before the international break.
Expanding more widely on the squad, he added: "[Matheus] França still with his fractured rib is out. Chadi with his knee injury now [is out]. I think everybody else is available."
The manager confirmed that no new signings have been registered by the midday deadline to take part in Sunday's fixture.
"No new player will be available for Sunday, but we trust in all the players who are here.
"We have a competitive squad, and the win against Norwich was important for their self-confidence – we could see it in training.
"The players are smiling more, the mood went up, so this is what we now want to continue at Chelsea and before many go to their national teams again."