Kyle Shanahan experienced a first as an NFL head coach in the 49ers’ 12-6 loss to the Los Angeles Rams on Thursday at Levi’s Stadium when one of his players refused to take the field.

Linebacker De’Vondre Campbell’s role changed with the return of Dre Greenlaw this week, and when he left the game in the third quarter with soreness in his Achilles tendon and knee, Campbell refused to play when Shanahan asked him to take Greenlaw’s spot to take and instead went to the locker room.

“He said he didn’t want to play today,” Shanahan told reporters after the game, noting that he had never had that happen to a player before. “…He was going in when Dre came out.”

Ten months after tearing his Achilles tendon in Super Bowl LVIII, Greenlaw returned to action in Week 15. The 49ers signed Campbell to a one-year contract in NFL free agency this offseason to make up for Greenlaw’s absence. The former All-Pro linebacker was drafted by the Atlanta Falcons in 2016 when Shanahan was the team’s offensive coordinator.

Shanahan did not say whether the 49ers will release Campbell following his actions on Thursday.

“We’ll figure something out, but I don’t know right now,” Shanahan said.

Campbell’s teammates didn’t mince words when asked about the linebacker’s decision not to play.

“I mean, he’s a professional. He’s been playing for a long time. If he didn’t want to play, he shouldn’t have taken his clothes off,” cornerback Charvarius Ward told reporters in the locker room. “He could have told (them) that before the game. So I feel like it was stupid for him to do that, which definitely hurt the team because Dee (Winters) was out and we needed a linebacker and I think (Demetrius Flannigan-Fowles) was also devastated.

“The fact that he does that is, in my opinion, nonsense. It will probably be canceled soon. That’s what it’s all about.”

Tight end George Kittle didn’t learn of Campbell’s departure until after the game, but said he wished he had known while the 49ers were still on the field.

“Look, if you’re in the squad and you’re getting fit, you’re expected to play,” Kittle told reporters. “I think anyone in this building who is asked to go in, I think 100 percent of everyone would die to get on that football field. People go through random things off the field, I can’t comment on that. Whatever’s his.’ The decision was that it wasn’t for this organization, for this team, and that’s on him. I’m not very happy about it.

“Is that why we lost? Absolutely not, but it’s hard to win football games when someone doesn’t want to play football…especially when you lose two linebackers and another one could have passed.”

The unique situation comes as San Francisco fell to 6-8 this season, which was nothing short of frustrating. But Shanahan is confident the locker room is as tight as ever – and supports his coach.

“I didn’t lose anyone,” Shanahan said. “Someone doesn’t want to play football, it’s very simple. (I) think our team and I know what we think about it, so I don’t think we need to talk about him anymore.”

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