Chiefs quarterback Brady Quinn is being evaluated for a possible concussion and his status for Thursday night's game at San Diego won't be known until later in the week.
Coach Romeo Crennel said Monday that Quinn will start against the Chargers if he's cleared to play. Otherwise, Matt Cassel will be back under center for the Chiefs.
"Just depends on what the doctor tells me," Crennel said. "If the doctor tells me he can go, he can do. If the doctor tells me he can't go, he can't go."
Quinn was hurt in the first quarter of Sunday's 26-16 loss to the Oakland Raiders, though it's unclear when the injury occurred. He was sacked by Rolando McClain and then took another shot while floating a pass that was picked by Matt Giordano.
He left the field and went down the tunnel leading to the locker rooms, and Crennel said a trainer told him at that point that Quinn had sustained a "head injury" and was unavailable.
Crennel said that Quinn wasn't at the practice facility Monday while he underwent tests, and Cassel would run the first-team offense during a walk-through practice.
"Cassel will take those turns, but then when the doctor lets me know I'll make a decision," Crennel said. "If he's healthy and he can go, he'll go. We'll wait to see what happens."
Quinn was making his second straight, the first having come at Tampa Bay, when Cassel still had not been cleared to play following his own concussion sustained against Baltimore.
Crennel said during the Chiefs' bye last week that he would stick with Quinn even though Cassel was ready to go because he wanted to send a charge through the team.
Things didn't go well for either of them Sunday.
Quinn only completed two passes for a single yard with the interception before he was knocked out of the game. Cassel was 20 of 30 for 218 yards with a touchdown and an interception.
The two picks were among four turnovers by the Chiefs.
"I thought during the bye week I did something radically different to try to change the team, and that change got hit in the head," Crennel said. "You just have to go forward."