Cesar, who was heavily linked with a move away from Loftus Road during the close-season following QPR's relegation from the Premier League, sustained the injury in training on Tuesday and is expected to be sidelined until the end of October.
The former Inter and Flamengo star has not featured for QPR this season, with manager Harry Redknapp admitting prior to Wednesday's goalless draw with Brighton that he 34-year-old is not in his plans and facing a tricky dilemma as Cesar has one eye on next year's FIFA World Cup in his home country.
He said: "It's a difficult situation with Julio and I'm surprised no one came in for him (during the transfer window).
"I don't know whether Julio wants to sit on the bench. His dream is to play in the World Cup in Brazil and I don't think this will affect his situation.
"The manager of Brazil thinks he's the number one man and I don't think anything that happens at QPR is going to change that for him."
QPR have also been dealt an injury blow after it was confirmed that striker Bobby Zamora has undergone surgery on a knee problem that will rule him out until the end of December.
