The results of the MRI will not be available until Tuesday, but Prince's status for the Bruins' game Thursday at Oregon (No. 2 BCS, No. 1 AP) is uncertain.
"It wasn't necessarily getting better," Prince said Monday night. "It hasn't been improving as fast as we would have liked it to, so they just want to look at it to make sure we get a good picture of what is going on in there and to make sure that nothing is changed, and if it has, then how to fix it."
Prince originally injured his knee during UCLA's victory over Texas on Sept. 25. He sat out the following week against Washington State but returned and started against California. He has practiced during the bye week but has taken periods of rest. On Sunday, he participated fully and said he might have aggravated the injury.
"Practice [on Sunday] wasn't the best thing for it," Prince said. "We figured that resting would probably be better than aggravating it even further [Monday]."
Brehaut started the Washington State game Oct. 2 and guided the Bruins to a 42-28 victory. It was UCLA's highest scoring output of the season, and Brehaut completed 12 of 23 passes for 128 yards -- the most by a UCLA quarterback this season.
"I can't control the coaches and what their decisions are," Brehaut said. "I can't control how Kevin's leg feels. I can only control how I go out every day and prepare. So that's really what I try and work on. I don't worry about all the outside stuff -- who is getting the nod or whatever."
Offensive coordinator Norm Chow said that even if a decision has been made on a starting quarterback for Thursday's game, the Bruins would be unwise to announce it.
"If we say Richard is that starter, they go watch the Washington State tape," Chow said. "Now, they're not sure and they're going to look at all the tape. We would be foolish to give away our guy now."
Peter Yoon covers UCLA football for ESPNLosAngeles.com.