Packers coach Mike McCarthy said Monday that Barnett tore a right knee ligament in Sunday's game against the Minnesota Vikings, which the Packers lost 28-27, but he wouldn't specify if it was an ACL tear. Surgery has not yet been scheduled.
"We've lost Nick Barnett for the season because of a ligament tear in his knee," McCarthy told the Green Bay Press-Gazette. "So, we just got the word here about a half-hour ago. He's very disappointed. It's unfortunate. But we need the other guys to step up."
It's a major blow to an already-suspect run defense, which gave up 192 yards rushing to Vikings running back Adrian Peterson on Sunday.
McCarthy said the coaching staff hasn't decided who will start in Barnett's place.
"Well, that's what we're talking about," he told the Press-Gazette. "We talked about it as a defensive staff this morning, the potentials. Obviously, Desmond Bishop. A.J. Hawk, and Brandon Chillar also factors into that, too, so we'll probably make that call [Tuesday]."
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."
Vikings running back Chester Taylor turned a short pass into a 47-yard touchdown on the next play after Barnett's immediate replacement, Bishop, blew the coverage.
"I definitely could've done better," Bishop said after the game. "The touchdown I gave up was bad."
Information from The Associated Press was used in this report.