Muhammad, the crown jewel of UCLA's top-ranked 2012 recruiting class, was injured in practice Wednesday.
The Bruins open their season Nov. 9 against Indiana State, so there is a chance Muhammad, a dynamic and athletic scorer who already is projected as an NBA lottery pick, could be recovered in time to play in that game.
However, a pending NCAA investigation regarding Muhammad's amateur status still might keep him out. There is no timetable for the NCAA to rule on his eligibility.
Fellow Bruins freshman Kyle Anderson is facing a separate NCAA review.
The Bruins, ranked No. 13 in the preseason coaches' poll, play in the Legends Classic on Nov. 19-20 at the Barclays Center in New York. They face Georgetown in the semifinals and have a possible matchup with preseason No. 1 Indiana the following day.
Earlier this week, the Bruins lost forward David Wear to an ankle sprain, and two weeks ago, guard Tyler Lamb had surgery to repair cartilage in his knee. Wear is expected back next week, and Lamb should return early next month.