The 49ers suspended linebacker De’Vondre Campbell for three games — ending his regular season — after the nine-year veteran refused to enter Thursday night’s game against the Rams.

Head coach Kyle Shanahan told reporters Campbell said he didn’t want to play in the NFC West clash when called upon in the third quarter, with the All-Pro subsequently walking off the field and to the locker room at Levi’s Stadium in Santa Clara.

On Monday, GM John Lynch announced the suspension, officially “due to conduct detrimental to the team.”

The issue arose after the 31-year-old Campbell lost his starting spot due to the return of Dre Greenlaw, who was then injured in Thursday’s game.

The 49ers had also lost Dee Winters to a back injury.

“His actions from the game is just not something you can do to your team,” Shanahan said Friday, adding that he’s never been in that position as a head coach.

The team opted not to cut Campbell for financial reasons — preventing him from catching on with another team — and will not have to pay him for the remaining three regular-season games,

San Francisco tight end George Kittle and cornerback Charvarius “Mooney” Ward explained their frustration with Campbell after the 12-6 loss to the Rams.

“It’s just dumb. It’s just stupid. It’s very immature,” Kittle said. “I just don’t see how you could do something like that to your team… I’ve never been around anybody that’s ever done that and I hope I’m never around anybody that does that again.”

Ward said that Campbell refusing to play was “some sucka s–t” and that he “hurt the team” because the 49ers were short at the position.

Campbell has yet to address the incident or suspension.

The 49ers signed Campbell to a one-year deal as an unrestricted free agent in March after three seasons with the Packers.

Campbell started 12 of 13 games for the 49ers entering Thursday’s contest, but the team had been phasing him out for Greenlaw’s return.

The 49ers (6-8) face the Dolphins (6-7) in Miami on Dec. 22.