LOS ANGELES -- USC defensive lineman Armond Armstead is likely to be sidelined for six weeks after breaking his left foot in a morning practice, adding to an uncomfortably long list of early injury setbacks for the Trojans.
USC already has lost fellow defensive lineman Averell Spicer, center Kristofer O'Dowd and quarterback Aaron Corp to minor injuries during camp, possibly hindering their progress in replacing 10 starters from last season's Pac-10 champions.
Armstead was hurt when safety Shane Horton accidentally stepped on his foot during drills. The 295-pound sophomore had been working out with the Trojans' first-team defense, and was expected to win a starting spot at defensive end.
"It's going to be a good six weeks before he gets back," coach Pete Carroll said. "We've had guys who had that injury before, and it's hard to beat that time frame, so we'll see. Being a big guy, it's tougher coming back than a lighter guy."
Freshman lineman Wes Horton replaced Armstead for much of the afternoon practice, but several players will be in competition for the spot. Derek Simmons and Malik Jackson also have played Armstead's position during camp.
"I'm a little faster, able to get off the ball quicker," Wes Horton said. "I'm not going into it thinking I'm the starter ... [but] this train is going to keep on moving."
Armstead, who watched Thursday's afternoon practice on crutches, will undergo surgery Friday to insert a screw in his foot. The Sacramento native has never had surgery before, but has no doubts about a quick recovery.
"They said six weeks, so I'm going for four," Armstead said. "I thought I was having a good camp, was getting better and better."
The Trojans already lost Spicer, their presumptive starting defensive tackle, to a sprained ankle last week. Spicer likely will return before the season opener against San Jose State on Sept. 5, but the injuries don't help USC's progress in replacing at least six starters in the defense's front seven this season.
"My approach has always been to get everybody ready to play, so anybody can step in," defensive line coach Jethro Franklin said.
Corp took another step forward in his return from a broken bone in his left leg Thursday, looking sharp in a throwing drill. The sophomore is expected to resume running this weekend, and plans to return to practice next week to challenge Matt Barkley and Mitch Mustain for the starting job.
O'Dowd, considered one of the nation's top centers, isn't certain he'll be ready to return from his dislocated kneecap by Sept. 5. He's determined to play the following week at Ohio State, however.
Freshman safety Patrick Hall, one of the nation's top defensive recruits, also could miss the season with a knee injury, Carroll said. Hall was hurt early in his first practice with the Trojans on Wednesday after sitting out the early days of training camp with academic issues.