Mitrovic has been in fine form for Fulham this season, scoring nine goals in 12 Premier League games.
Mitrovic sat out Fulham's 2-1 defeat to Manchester City last week and is also unavailable for Sunday's home game against Manchester United.
Silva maintains Mitrovic's absence puts his availability for the World Cup in doubt even though he has been named in Serbia's 26-man squad.
"What I can tell you is that it will be a decision made probably in the first days of next week, between the [Serbia] medical staff and our medical staff," Silva told reporters.
"That will help decide what is the best decision for him, and for us as a club as well because he is really important.
"I'm not the right person to say now whether he will be fit or not to be there.
"What I know right now is that he wasn’t ready for the last match and will not be ready for the next one, unfortunately for us.
"What I can also tell you is that he cannot be harmed. He cannot be harmed for something that will come from the decision."
Serbia are in the same group with Brazil, Cameroon and Switzerland in Qatar.
Mitrovic is his country's all-time leading goalscorer with 50 goals in 76 caps.
