The 5-foot-9, 210-pound Lamb had four carries for 13 yards and added a 20-yard kickoff return during the 49-7 victory over the Bobcats.
U of L coach Charlie Strong announced the injury on Tuesday during his new conference. He had said on Sunday the Cardinals' didn't have any significant injuries, but added they went back and re-checked Lamb and found the injury.
" We checked Corvin and he ended up tearing his ACL late in the game," Strong said. "I am not exactly sure when he will have surgery."
Strong said the rest of the team had some bumps and bruises but that Lamb was the only serious injury.
"It's tough," Lamb said. "When a young man has put so much into it and worked so hard, you never want to see any injury happen."
Strong said "we had five running backs and now we have more," with Senorise Perry, Michael Dyer, Dominique Brown and Brandon Radcliff now holding down the fort in the backfield for the Cardinals.
U of L ran for 199 yards in the opener.