Johnson is expected to have surgery on Thursday, according to school officials. Ole Miss coach Hugh Freeze said Johnson's recovery time is expected to be about three months.
The 6-foot-3, 233-pound junior played in all 13 games last season and led the Rebels with 6½ sacks last season.
Freeze said in a statement that injuries "are a part of the game" and that the coaches "hate it for the kids." Johnson is part of a nucleus of young defense linemen — including Issac Gross, Channing Ward and Woodrow Hamilton — that had some success last season as the Rebels finished with a surprising 7-6 record.