With Cutler back in Chicago out with a concussion, Marshall caught just two passes for 21 yards which included the Bears' only score, an 8-yard touchdown in the third quarter. After missing a pass near the sideline from Jason Campbell, Marshall turned his anger toward a teammate.
"I'm a grown man," Marshall said he told the unnamed teammate. "That's the big line that a lot of us like to use," he later admitted.
Cutler acknowledged Marshall probably benefits from Cutler's presence on the sideline during games.
"When I'm there I think things go a little bit smoother for Brandon," Cutler said Tuesday on "The Jay Cutler Show" on ESPN 1000. "He's a receiver. He's like any high-end receiver; they want the ball and when they don't get the ball they get frustrated and when they get frustrated they get mad.
"That's why I've always said, if you've got a big-time receiver and they make plays for you, just throw them the ball. I don't care if they are covered or not, just throw them the ball and they will be happy."
Marshall entered Monday's game among the NFL's most targeted receivers, but saw just four passes come his way. He said the 49ers "tried to take me out" by playing two-man and admitted "I have to do a better job of just trying to beat double coverage and look at some different techniques and ways I can get open."
It was believed that Marshall became involved in an altercation with Matt Forte after the play, but the receiver denied he and the running back verbally sparred.
"No, it wasn't Matt. It was actually another guy," Marshall said. "After that play on the sideline, I was a little frustrated because I didn't make the play. They told me to get back, and I actually hurt my shoulder. So I was telling the guy I hurt my shoulder.
"I actually told them, 'I'm grown.' It was one of those games where things were going wrong for us. I have to do a better job when I'm frustrated of not letting it show. I definitely let the team down. I should've made that play, and I didn't."
Marshall needs just 75 yards to become the first Bears 1,000-yard receiver since Marty Booker in 2002. Despite the off night, Marshall is stil laveraging 6.9 catches and 92.5 yards per game.