The injury is similar to that sustained a year ago by Louisville quarterback Brian Brohm, who missed two games after being hurt during an early season game against Miami.

Stull, a junior from Pittsburgh, was hurt when his thumb was bent backward on a handoff during the third quarter of a 24-3 victory over Eastern Michigan on Saturday night.

Before that, Stull was 14-of-20 for 177 yards and a 21-yard touchdown to Oderick Turner. He threw only 10 passes a year ago as a backup to Tyler Palko.

Stull's injury seems certain to sideline him for games Saturday against Grambling, Sept. 15 at Michigan State and possibly longer. It also creates the possibility that coach Dave Wannstedt may decide to play freshman Pat Bostick immediately, rather than red-shirting him as planned.

"We will work this week to get Kevan Smith and Pat Bostick ready to play against Grambling," Wannstedt said Sunday. "Their performances at practice will determine our starter for Saturday."

Bostick, who missed the first week of Pitt camp after leaving campus unexpectedly for personal reasons, is considered to be more talented than Smith.

Smith, a redshirt freshman, was 2-of-4 for 18 yards Saturday after replacing Stull. He is convinced he can handle the job with Stull out.

"I have confidence in myself and I think the other guys believe in me 110 percent," said Smith, who played at Seneca Valley High near Pittsburgh. "If I have to start next week, I'm ready."

Stull was hurt after getting off to a strong start, hitting his first seven pass attempts. He is not considered to be as strong a playmaker as Palko was, but Wannstedt likes how Stull runs the team and makes minimal mistakes during practice.

"We feel very disappointed for Billy," Wannstedt said. "He worked incredibly hard during the offseason to earn the starting job and those efforts showed in his strong play. Knowing Billy, he will be very diligent in his rehabilitation and will be back as soon as possible."

Bostick's absence from camp was never fully explained by Pitt, and few quarterbacks can adjust to the complexities of college football only a year after they were playing high school football.