A serious injury was immediately feared, and it derails Davis' most successful season in another blow for injury-plagued Carolina (3-5).
"He's played very well. I feel bad for the young man because he's put a lot into it," coach John Fox said before the team revealed the extent of the injury. "He was playing at a high level. It's unfortunate, and I feel bad for him and his family."
Davis is the second defensive starter to be lost for the season, joining Maake Kemoeatu (torn Achilles' tendon), who went down on the first day of training camp.
Davis missed much of training camp with a sprained medial collateral ligament in the same knee, then sat out the Buffalo game last month with a hamstring injury.
Landon Johnson, who led Cincinnati in tackles three times over four seasons but has been much less productive in two seasons with Carolina, will likely move into the starting lineup. Johnson had 10 tackles against the Bills.
The Panthers did not immediately place Davis on injured reserve, which would open a roster spot for another linebacker.
Copyright 2009 by The Associated Press