Lamar, a senior, was injured early in the fourth quarter of Saturday's game versus Syracuse, Coach Skip Holtz said.
"It'll be a blow to us offensively, with the productivity he's had in the last two weeks, rushing for  yards," Holtz told the Tampa Bay Times. "We're definitely going to miss that production, and we're going to have to make it up."
Junior tailback Marcus Shaw and senior Demetris Murray are expected to rotate carries in Lamar's absence, the Times said.
Exploding whale video goes viral on Internet
Texas principal bans speaking Spanish, stirs controversy