Detroit Lions running back David Montgomery will sit out the rest of the season after sustaining a sprained MCL in Sunday's 48-42 loss to the Buffalo Bills, coach Dan Campbell said Monday.

Montgomery is undergoing additional testing on his knee and getting a second opinion, sources told ESPN's Adam Schefter.

"Looks like he's going to require surgery that'll put him out for the rest of the year," Campbell said. "He had gotten it at some point yesterday in that game.

"I mean, David's so tough. He continued to play through and then got it checked out today and realized that's what it was. He's just the ultimate teammate, ultimate competitor. We're going to miss him, man."

Montgomery is one of several key players who were injured Sunday, including several important defensive players. Lions starting defensive tackle Alim McNeill sustained a torn ACL, ending his season, and starting cornerback Carlton Davis III sustained a fractured jaw in the loss, sources told ESPN's Adam Schefter. Davis will undergo surgery and be sidelined indefinitely, the sources said.

The Lions also lost cornerback Khalil Dorsey to a season-ending ankle injury in Sunday's game. Dorsey underwent surgery after the game.

The injuries to McNeill, Davis and Dorsey are the latest setbacks to a Lions defense that had 13 defensive players on the injured reserve list entering Sunday's game. That includes star defensive end Aidan Hutchinson, who sustained a fractured tibia and fibula in Week 6.

"Those guys helped us get to this point, so we owe it to them," Campbell said. "They laid it on the line for us."

Montgomery is second on the Lions with 775 rushing yards and leads the team with 12 rushing touchdowns. He also has 36 receptions for 341 yards. He signed a two-year, $18.25 million extension with the Lions in October. 

Montgomery is part of the Lions' one-two punch at running back with Jahmyr Gibbs, who leads the team with 1,047 rushing yards and has scored 14 total touchdowns (11 rushing).

McNeill signed a four-year, $97 million extension earlier this season and helped stabilize Detroit's defensive line after Hutchinson's injury. He finishes the season with 25 tackles and 3.5 sacks.

Davis, acquired in an offseason trade with the Tampa Bay Buccaneers, has 2 interceptions, 11 passes defensed and 56 tackles this season. He will be an unrestricted free agent after the season.

The loss to the Bills ended the Lions' 11-game winning streak. The Lions (12-2) still are in the top spot in the NFC playoff bracket, holding the tiebreaker over the Philadelphia Eagles (12-2) based on winning percentage in conference games, with three games to go.

Campbell doesn't want the team to be caught up in the injuries, but to remain focused on finishing this season strong.

"We acknowledge the fact that we've lost players, we've lost really good players, but nobody cares," Campbell said. "Nobody cares and nobody's going to give us a pass or put an asterisk next to your record.

"So, what it means is some guys are going to have an unbelievable opportunity. Because of what has happened, that means now, if you're a guy who's on the vet squad, or you're a young player or you're somebody that's been dying to get an opportunity, you're about to get it."