49ers QB Steve Young will miss at least a week and possibly more because of his latest concussion, but tests showed no signs of more serious brain trauma, his agent, Leigh Steinberg, said yesterday.

Young took a frightening hit midway through Monday night's game at Arizona and left with his fourth concussion since 1996. He underwent an MRI yesterday.

"The MRI did not show any of the so-called white spots, which are thought to be indicative of progressive brain trauma," Steinberg said. "But the doctor did recommend he sit out at least a week and possibly two."

Coach Steve Mariucci confirmed that Young would be sidelined for a minimum of one week, leaving backup Jeff Garcia in position to make his first NFL start Sunday against the Titans. Steinberg said he spoke to Young and that the quarterback intends to return as soon as possible. He said Young has no intention of retiring.

"Steve is not in denial in terms of this concussion issue. He will follow the medical advice," Steinberg said. "He obviously has tremendous opportunities for life after football and he's not going to endanger that."

NEWS & NOTES: Dolphins Coach Jimmy Johnson placed rookie Dimitrius Underwood on the reserve, non-football injury list, assuring Underwood will not play football this year. Underwood slashed his neck with a knife Sunday. . . .

Cardinals WR Rob Moore aggravated a pulled hamstring early in Monday's loss to the 49ers and will be out indefinitely.

"He's going to be out for a significant amount of time," Coach Vince Tobin said.