Cutler suffered a concussion Sunday night on an illegal hit by Houston Texans linebacker Tim Dobbins. He did not immediately display the symptoms of a concussion after Dobbins' hit and stayed in the game for an additional seven plays before being ruled out at halftime. Dobbins was fined $30,000.
Bears rookie defensive end Shea McClellin, who also suffered a concussion Sunday, will be held out Monday night as well.
"It feels good to get back in there and play, but you never want to have the opportunity to play because of someone's injury. But we understand the position we play; those things occur sometimes," said Campbell, who said he was told he would start before Thursday's practice.
Campbell hasn't started a game since Oct. 16, 2011, when he suffered a broken collarbone with the Oakland Raiders.
"It's a tough opponent we have Monday night," Campbell said. "No one said it's going to be easy, but we have to go there and fight together and we have to play as a unit. You have to let it hang out in a game like this. We have all the respect in the world for the 49ers and what they do, especially on the defensive side of the ball. It's a big part of the reason why they were in the NFC Championship Game a year ago. Utmost respect. We understand it's going to take a total team effort."
Campbell is confident, but he's also realistic.
"Everyone knows if you haven't played in a while, you're not going to be like a Peyton Manning," he said. "You have to do what you do and do it to the best of your ability. Jay is good at what he does and I'm good for different reasons for things that I do. That's the way I have to play the game."
Cutler's chemistry with receiver Brandon Marshall, going back to their days with the Denver Broncos, has been one of the reasons the Bears are 7-2. But Marshall is confident the Bears can win with Campbell, who was brought in after the team collapsed last year after a Cutler injury. The Bears went from 7-3 with Cutler to finish 1-5 and out of the playoffs as Caleb Hanie struggled in a backup role.
"If you look at what happened to the Bears last year, that's why he's here," Marshall said. " He has a big arm, and he has a great feel for the game.
"Jason's played a lot of football, he's an established vet, he's the next guy up and more than capable. We're fortunate enough to have a starting quarterback as our backup.
I'm excited and really at ease to have him in our huddle, because he makes it so much easier."
Offensive coordinator Mike Tice has been impressed with Campbell in practice.
"He's played before and watching him in practice he brings tremendous poise and leadership to the guys," Tice said. "The guys have rallied around him.
"He's had two good rhythmic days of practice. I like the things he is doing. Certainly, he has his thoughts on the things he likes in the plan and the things he doesn't like in the plan. As always we try to communicate with our players the best way we can so we're out there calling things they feel good about, that they can execute properly. I probably haven't just called enough of those things, right? I'm pleased he's a good player and a good person, too."
Campbell relieved Cutler in the second half against the Texans and completed 11 of 19 passes for 94 yards and had one rushing attempt for five yards. Campbell started 70 games for the Washington Redskins and Raiders from 2006-11 but signed a one-year deal with the Bears in the offseason to serve as Cutler's primary backup.
"Last week's game was good for me knowing I have to play this week, to get those reps against a really good defense in Houston, and get your feet wet and get moving again," Campbell said. "To get those reps was huge."
Bears head coach Lovie Smith wouldn't say whether Cutler has been medically cleared or whether Cutler will travel with the team to San Francisco.
"He's not playing this week and that's about as much as I'm going to go into it," Smith said. "He's getting better and we're hopeful for next week. I think that should be enough for you all to go on right now."