He did not return to the game after sustaining the injury in the second quarter.
Nkemdiche, one of the top players in college football, usually stars on the defensive line for Ole Miss, but was injured as a ball carrier in a short-yardage situation. He had two rushing touchdowns on three carries entering the game.
NFL Media analyst Chad Reuter rated Nkemdiche, a junior, as the No. 6 player in all of college football in his midseason ranking of CFB's top 20 players earlier this week.
Losing for Nkemdiche for an extended period of time would be a huge blow to the Rebels (5-2). They still have only one conference loss (to Florida), but falling to Memphis severely damages their playoff hopes, perhaps beyond repair, with a big home game against Texas A&M looming next week.