Alameda, Calif. ? Rich Gannon was scheduled to undergo an MRI exam Tuesday on his ailing shoulder, and Oakland coach Bill Callahan would not guarantee the quarterback’s starting job until the results were known.

Gannon, last season’s league MVP, was pounded by the Kansas City defense in the first half of the Raiders’ 17-10 loss to the Chiefs Monday. He was held out of the second half because of a bruised right shoulder.

Callahan praised Gannon and backup Marques Tuiasosopo Tuesday, but said he was not yet sure who would be the Raiders’ first-string quarterback when the team returned from its bye week.

“I’m not going to make any determination on the quarterback’s play until I know about his health situation,” Callahan said of Gannon. “This is the league’s MVP. I have great respect for him and everything he has done for the team.”

After he was sacked by linebacker Shawn Barber on the final play of the first half, Gannon went to the sideline holding his arm. Gannon, 10-of-19 for 58 yards and an interception, received treatment on the sideline while Tuiasosopo played the second half.

Tuiasosopo, a seldom-used backup who had just 69 yards passing in his career, rallied the Raiders to three lengthy drives and 10 points in the fourth quarter. But the comeback attempt ended when two Chiefs tackled Tim Brown at the Kansas City one-yard line as time expired.

Gannon has been the focal point of an offense that led the league in many statistical categories last season. He made his fourth-straight Pro Bowl last season after leading the NFL with 4,689 yards passing while setting league records with 418 completions and 10 300-yard passing games.

But the 37-year-old quarterback has been mostly terrible this season along with his teammates as Oakland stumbled to a 2-5 start. With a dismal passer rating of 73.5, Gannon has thrown for just 1,274 yards with six touchdowns and four INTs.