Thomas, a redshirt junior, was in a battle to start at defensive tackle after the departure of Ego Ferguson and Anthony Johnson from last season's team. He was expected to win the job.
LSU hasn't confirmed the injury, but according to the report, Thomas wasn't seen at practice Thursday or Friday.
A native of Breaux Bridge, Louisiana, Thomas played in 11 games last season, recording nine tackles. He made his first career start in the Outback Bowl when Ferguson was unable to play in the game.
In Thomas's absence, Greg Gilmore, Frank Herron and Maquedius Bain will likely compete for the starting job.
LSU opens the season Aug. 30 against Wisconsin in Houston.
- Ben Estes