The St. Louis Rams will be without quarterback Marc Bulger for three to six weeks because of fracture in the upper part of his shinbone. An MRI exam Monday disclosed the damage — technically called a tibial plateau fracture. It occurred Sunday in the 21-13 loss to the Arizona Cardinals at the Edward Jones Dome.

Coach Steve Spagnuolo said the injury does not require surgery. “It’s just crutches. He’ll have to say off it for a while,” he explained.

That means that Kyle Boller takes over as the first-team quarterback and rookie Keith Null moves up to No. 2. Boller started two games earlier in the season, after Bulger bruised the rotator cuff in his right (throwing) shoulder.

Bulger also had an MRI exam Monday for an injury to his groin-hamstring area, which has been diagnosed as a strain, Spagnuolo said. Bulger is scheduled for a neurological exam, too, because he took a blow to the head late in the game.