USC starting center Matt Spanos went down Tuesday in practice with a torn triceps while trying to block nose tackle Sedrick Ellis.
Spanos is expected to be out two to four weeks, according to USC offensive line coach Pat Ruel.
A day after tabbing left guard Jeff Byers as the replacement for injured center Matt Spanos, USC has opted to keep Byers at guard and insert true freshman Kristofer O'Dowd as its starting center for Saturday's opener against Idaho. O'Dowd would be the first true freshman center to ever start for the Trojans.
On Wednesday night Ruel, who was raving about O'Dowd, was asked if he had picked things up as fast as any freshman lineman he's worked with. Ruel said he didn't want to go that far, but 24 hours later, he named O'Dowd as his starter because it would only mean moving one lineman, not two.
O'Dowd will become only the third true USC freshman to start in the last 60 years, joining Travis Claridge and Brad Budde.
After Wednesday's practice, Ruel said the new lineup actually produced one of the better days the Trojans' front has had this month. "We were communicating a lot better [Tuesday]," Ruel said. "I really think the responsibility was heightened."
Idaho doesn't figure to pose any problems for the Trojans, who have a bye week before their much-anticipated Sept. 15 game at Nebraska. In that game, USC could certainly use the 6-foot-5, 305-pound Spanos, who Ruel pegged as a powerful, aggressive pivot man as compared to the more finesse style of Byers.
Top-ranked USC may be loaded, but the one area where the Trojans aren't so deep is on their offensive line.
"Everybody has to play everything right now," coach Pete Carroll said, "everybody that has any background in another spot."
The key spot though, is right in the middle.
The 6-4, 285-pound Byers, who came to USC as a center, has experience playing the position, but has struggled there in the past. Last season when USC's All-American center Ryan Kalil wasn't on the field in practice, the Trojans had trouble just getting the ball snapped. Ruel, though, says Byers has worked hard and hasn't had any of those problems this fall.
In other USC injury news, freshman running back/kick returner Joe McKnight has been cleared for contact and will play against Idaho. On Wednesday, he wore a large brace protecting the sprained MCL in his right knee and said it has been hard to deal with it. "The brace limits me a little bit, because I really can't do hard cuts off my right leg," he said. "When I get my sleeve tomorrow, I'll be able to do all that stuff."
Carroll said McKnight would definitely play against Idaho. "He looked great on film yesterday; he looked fine today; he'll definitely play in the game," he said.
Bruce Feldman is a senior writer at ESPN The Magazine.