USC coach Pete Carroll said after practice today that Sanchez was injured in a scrimmage Sunday night at the Los Angeles Coliseum.

"It's going to be close, the way I understand it," Carroll said regarding whether Sanchez, the second-stringer behind John David Booty, would be able to play Sept. 1 against Idaho at the Coliseum.

But, Carroll added: "It might be a week."

Carroll said that Sanchez wasn't sure how he hurt himself, saying the 6-foot-3, 225-pound third-year sophomore from Mission Viejo continued to play after being injured until his right thumb became numb.

Sanchez completed 4-of-8 passes for 29 yards with one interception in the scrimmage. He completed 3-of-7 for 63 yards while appearing briefly in six games last season.

Carroll said Michael McDonald, a 6-2, 185-pound senior from Newport Beach, will work as the second-stringer for now, but Aaron Corp, a 6-3, 185-pound freshman from Villa Park, would get plenty of reps in practice.

"The way we look at it, this is a tremendous opportunity for Aaron Corp," Carroll said. "It's so hard for him, for anybody at this point. But Aaron's handling it well."

Corp completed all four of his passes for 49 yards in the scrimmage, and McDonald was 1-for-2, throwing a 50-yard touchdown pass to Cooper Stephenson.

Corp completed 212 of 311 for 2,750 yards and 21 touchdowns with seven interceptions and rushed for 1,197 yards and 12 more TDs as a senior at Orange Lutheran High last season, leading his team to a 14-1 record.