The defensive lineman sustained a season-ending anterior cruciate ligament injury during Sunday's victory at Philadelphia, the latest in a long line of significant ailments for Green Bay's first-round pick in the 2007 draft.
Harrell has played in just 13 regular-season games in his first three years, missing much of 2008 and all of last season with back problems. Still, he made the Packers' roster coming out of training camp.
"Justin has had a tough go from a medical standpoint," Packers coach Mike McCarthy said Monday. "I've seen players in this league sometimes have injuries in bunches and then they're able to overcome them and go on to have a good career, and I was hoping Justin would fall into that category, and now he has another hurdle that he has to get over."
The team didn't disclose which knee was injured, but McCarthy said Harrell will be placed on injured reserve, ending his season. He is under contract through the 2012 season.
The Packers also will be without running back Ryan Grant for at least a week after he sustained what McCarthy called a "significant" ankle injury that involved ligament damage.
Grant, who was wearing a protective walking boot on his right foot after the injury, said after Sunday's game that his ankle was just sprained, not broken.
"They made the decision to take me out," Grant said. "They didn't want to make it worse than it was. Once I'd iced it for a while, they said 'We might as well put you in a boot.'"
Beyond that, defensive lineman Cullen Jenkins will continue to play with a cast after breaking his hand in Sunday's game.
The injuries at running back and defensive line hit two spots where the Packers don't have a lot of depth.
On the defensive line, Green Bay already was dealing with the loss of Johnny Jolly, who has been suspended for at least this season under the NFL's substance-abuse policy.
"As far as any roster moves, this is really preliminary," McCarthy said. "That's an ongoing conversation. Our personnel department, they're always grading tape and making lists and looking at different options."
Jackson, a second-round pick out of Nebraska in 2007, played well in Grant's absence Sunday. He rushed for 63 yards on 18 carries and caught two passes. McCarthy said Jackson also did a good job picking up blitzes.
"I feel Brandon Jackson carried the load yesterday," McCarthy said. "I think there's a lot of evidence right there, recent evidence that he's able to play all three downs, and he will have that opportunity this week."
Kuhn, meanwhile, scored a touchdown during the third quarter Sunday.
"John's done a very good job with his limited opportunities," McCarthy said. "Every time you put the ball in John's hands he's been productive, and we feel very good about him. He's our third halfback and now will be our second halfback going into Buffalo."
Copyright 2010 by The Associated Press