DETROIT -- The Lions held off on placing running back David Montgomery on the injured reserve list after he received a third medical opinion following an MCL injury in Sunday's loss to the Buffalo Bills.

A source told ESPN's Adam Schefter that Montgomery "might have avoided season-ending surgery" and there is "optimism [for a potential return] in the playoffs."

"It's about rehabbing and going from there," the source said.

Initially, Montgomery was feared to be out for the season before receiving additional testing. Earlier in the week, Lions coach Dan Campbell acknowledged that the team was leaning on doctors while in a "waiting mode" about his injury status.

"It is one of these injuries that's unique because you need to know is it stable? OK, is it fixed, or will it scar? And then be certainly stable for now and for later and then you've got to rely on him, like, 'Hey man, I'm good. I can do this,'" Campbell said on Wednesday. "So, it's a combination certainly the doctors then him as well, where he thinks he can go with it and can he protect himself and play at a high level. So, we're in a holding pattern, which as of right now is a positive."

Detroit has been bitten by the injury bug with a league-high 21 players currently on the injured reserve list, including 16 defensive players, which is also the most in the NFL this season.

Montgomery is Detroit's second-leading rusher with 775 yards and a team-high 12 touchdowns behind Jahmyr Gibbs, who has 1,047 rushing yards and 11 touchdowns.

Although Gibbs is disappointed by the injury, he has no worries picking up the slack in his teammate's absence. Montgomery has encouraged Gibbs to "keep hooping," while Campbell and the coaching staff remain confident in his ability as "our lead horse."

For Gibbs, his on-field mindset isn't changing without Montgomery.

"Basically, the same, it's nothing different," Gibbs said. "I've been doing this my whole life, so I don't look at it any differently."