"An MRI on quarterback Jason Campbell's injured left knee has revealed a sprain, and his playing status for Sunday's game against the Denver Broncos is uncertain, Raiders coach Tom Cable said Monday.

Cable first said Campbell's knee was fine, but a few minutes later the coach said "absolutely" when asked if he could envision No. 3 quarterback Kyle Boller starting against the Broncos.

How realistic that is will begin to crystallize Wednesday when Cable gets a look at regular starter Bruce Gradkowski (right shoulder) and Campbell in practice.

Gradkowski was injured during a victory over the San Diego Chargers on Oct. 10 and missed Sunday's loss to the 49ers.

Campbell was hurt in the first half against San Francisco but played all the way through. After completing five of his first seven passes, he missed on all but three of his next 14, finishing 8 of 21 for 83 yards and a 10.7 passer rating.

Boller, 29, has started 46 games during his seven-year NFL career. He last played in a regular-season game on Jan. 3 against the 49ers in a relief role for the St. Louis Rams. His last start came Dec. 6. He said he is ready as a starter or backup against the Broncos.

"I've pretty much stayed on top of it over the last six weeks," Boller said, "and that's part of your job. It doesn't matter if you're a starter, second-stringer or third-stringer. You have to always be into the game plan and doing just the same things the starter's doing."