Packers coach Mike McCarthy said Monday that linebacker Barnett tore a right knee ligament in Sunday's game against the Minnesota Vikings, which the Packers lost 28-27. Surgery has not yet been scheduled.

It's a major blow to an already-suspect run defense that gave up 192 yards rushing to Vikings running back Adrian Peterson on Sunday.

McCarthy said coaches were discussing plans to replace Barnett, including using backup Desmond Bishop or moving outside linebackers A.J. Hawk or Brandon Chillar to the middle.

Barnett was injured on the Vikings' first drive of the second half while trying to tackle Peterson.

"I shot downhill, fast, trying to get a shot on him, and he cut back," Barnett said after Sunday's game. "So I tried to cut, and it was just bad footing."