SANTA CLARA >> A day after De’Vondre Campbell Sr. refused to play and walked off the job, coach Kyle Shanahan made it clear Friday that Campbell won’t be returning to the team.

“We’re working through the semantics of exactly how to deal with it,” Shanahan said on a media conference call. “You heard from me last night and the players. His actions from the game are not something you can do to your team or your teammates and still be part of our team.”

Whether Campbell’s one-year, $5 million contract is terminated or he’s released or suspended, Shanahan only said the 49ers would handle it “appropriately.”

Campbell’s did not play a snap in Thursday night’s 12-6 home loss to the Los Angeles Rams, refusing to budge from the bench once the 49ers needed him in the third quarter to replace a fatigued Dre Greenlaw in the latter’s season debut.

Shanahan said he wasn’t aware of Campbell’s boycott until asking the defensive coaching staff over their headsets about it in the third quarter.

“I addressed De’Vondre and found out. It was pretty simple to see how he was,” Shanahan said. “Then we moved on with our lives after that.”

Campbell, who started in place of Greenlaw the past three months, walked off the field in the fourth quarter to the 49ers locker room, where he was gone once reporters entered to seek his still-unanswered motive for his in-game desertion. Shanahan said he did not order him off the field, nor did Campbell reveal exactly why he refused to play.

“Not sure exactly what led to him leaving the field,” Shanahan said. “Once I found out he wasn’t playing, I moved on to people we could count on.”

Teammates seethed over what they deemed Campbell’s “selfish” act to leave their defense in a lurch, seeing how Greenlaw’s troublesome left leg sidelined him after a 30-snap debut and Dee Winters’ first-half neck injury kept him from working as the No. 3 linebacker, a role that perhaps Campbell thought he deserved in this week’s demotion.

This could spell the end of Campbell’s nine-year NFL career that’s earned him $38 million. He’ll be gone before playing out the one-year, $5 million contract with the 49ers, who turned to him in mid-March after linebacker Eric Kendricks backed out of a deal and defected days later to the Dallas Cowboys in free agency.

Campbell, 31, never quite meshed as a linebacker tandem with All-Pro Fred Warner. Prior to Thursday night’s benching, Campbell was a full-time starter, although he was not in on the Week 3 opening snap at Los Angeles where the 49ers instead deployed five linemen and five defensive backs around Warner. Campbell’s 79 tackles rank second to Warner’s 106.

“We needed a starting-caliber linebacker to fill in for Dre until he got back. (Campbell) had ups and downs throughout the year,” Shanahan said. “He started off slow. He got more used to our defense and how we expect people to play, and he improved throughout the year.”

In the 49ers’ previous home loss before Thursday’s, they fell to another NFC West opponent, and Seattle Seahawks quarterback Geno Smith raced past Campbell for a go-ahead touchdown run in the final seconds of that 20-17 collapse on Nov. 17.

Campbell had at least seven tackles — and no more than eight — in five of his six final games, not counting Thursday’s boycott.