SANTA CLARA, Calif. — The San Francisco 49ers added quarterback Alex Smith to their injury report today, listing him as doubtful for Sunday's game against Arizona with another problem in his surgically repaired right shoulder.

Shaun Hill will be the backup against the Cardinals.

The 49ers didn't specify what was wrong with Smith, only saying the injury occurred without contact during practice Friday. Smith, the former No. 1 overall draft pick, was expected to back up J.T. O'Sullivan, who beat out Smith for the starting job in training camp.

"He will be consulting with his surgeon in Birmingham for treatment recommendations," coach Mike Nolan said in a statement. "At this time there are no specifics to the injury or a timetable."

Dr. James Andrews performed surgery on Smith in Alabama in December, about 2½ months after Smith's shoulder was separated on a sack by Seattle's Rocky Bernard. Smith attempted to play through the injury but struggled and eventually went on injured reserve in mid-November while trading public jabs with Nolan about the severity of his injury.

Running back Michael Robinson, the former Penn State quarterback, is likely to be the No. 3 quarterback.