Stupid, stupid and very immature.

That’s how 49ers tight end George Kittle described De’Vondre Campbell’s third-quarter meltdown when the All-Pro linebacker refused to play against the Rams on Thursday night after losing his starting spot.

“Whatever his decision was, it wasn’t for this organization, it wasn’t for this team and that’s on him,” Kittle said in his postgame press conference following San Francisco’s 12-6 loss at Levi’s Stadium. “I’m not very happy about it. I would have had something to say. I wish I had heard about it on the field, but I didn’t.

“Is that why we lost? Absolutely not… Try to win football games when someone doesn’t want to play football, especially if you’re well dressed. It kind of makes you depressed, especially when you lose two linebackers.”

The 49ers lost two linebackers on Thursday as Dre Greenlaw (knee) and Dee Winters (neck) left the game with injuries.

“It’s just stupid. It’s just stupid. It’s very immature,” Kittle said. “I just don’t understand how you could do something like that to your team.”

Kittle explained that the situation didn’t cause tension within the team and that Campbell – a ninth-year linebacker – made himself an outlier.

“(There is) no disbelief or separation as a team. This is a person who simply chose not to play for his teammates. I don’t think it makes our offense or our defense look like we’re falling apart, it’s more like one person making a, as (49ers cornerback) Mooney (Charvarius Ward) said, a selfish decision. And I agree with Mooney on that. I’ve never been around anyone who has ever done that and I hope I’m never around anyone who does it again.”

Ward said afterward that Campbell’s refusal to play was “some nonsense” and that he had “hurt the team” because the 49ers had already lost two linebackers.

“He’s a professional,” Ward said after the game. “He’s been playing for a long time. If he didn’t want to play, he shouldn’t have dressed up. He could have told them that before the game. I feel like that was some stupid thing he did. It definitely hurt the team. Dee went down and we needed a linebacker… For him to do that, I think it’s pretty stupid. He’ll probably be circumcised soon, so that’s what it is.”

When asked to do so in the third quarter, Campbell refused to enter the game and then went to the locker room with a towel over his head.

Head coach Kyle Shanahan turned to the 49ers’ Demetrius Flannigan-Fowles, who was the only healthy linebacker on the active roster.

“He said he didn’t want to play today,” Shanahan said of Campbell.

The 49ers signed Campbell as an unrestricted free agent from the Packers in March.

He started 12 of 13 games for the 49ers before Thursday’s game, but the team removed him from the roster due to Greenlaw’s return.

The loss was a devastating setback as the 49ers attempted to get back into the NFC West race. Instead, they now find themselves in last place and 2 1/2 games behind the division-leading Seahawks.

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