LOS ANGELES -- USC quarterback John David Booty, the heir apparent to former Heisman Trophy winner Matt Leinart, suffered back spasms Tuesday so severe that he may miss the rest of spring practice.
"His back just tightened up on him, locked up on him," head coach Pete Carroll said after practice Thursday night. "He's got real serious back spasms that are going to keep him out for a little bit."
Carroll did not rule out a disk problem or the possibility that surgery would be needed. Rest and time will provide the answers, he said.
"It [surgery] may be [an option] way down the road, if it doesn't correct," Carroll said. "It's not at all time to do that, to think that way. If after two weeks, it has not responded, then they have to think more seriously about what the next step is."
The spasms came on as Booty jogged from one drill to another in the Trojans' opening session of spring practice on Tuesday.
Redshirt freshman Mark Sanchez, expected to challenge Booty for the starting job, took over the first-team offense Thursday. Behind Sanchez is redshirt junior Mike McDonald and Kevin Livermore, who made the team as a walk-on earlier this month. Garrett Green of Chatsworth, Calif., the only quarterback in the 2006 signing class, attended practice Thursday.
"Obviously, the focus goes to Sanchez," Carroll said. "He gets a great opportunity to be in charge, run the whole thing. We'll just try to maximize that, get Mike McDonald some work and wait for J.D. to get better."
Sanchez, who described Booty as one of his good friends, said he will take over the team because he must.
"Just trying to champion the cause, champion the opportunity," Sanchez said. "Show the guys I can do it and let them know I'm a guy who can play."
Carroll said that Booty suffered back spasms in the fall of 2004, his freshman year, and that he had a pre-existing back condition when he arrived at USC from his hometown of Shreveport, La. "I don't know the results of of it. They're comparing his old MRIs to the one they took yesterday, so we'll find out," Carroll said.
Offensive coordinator Lane Kiffin said he does not expect Booty back this spring. Booty undergoes surgery, Kiffin said, doctors expect he would be ready to practice by July.
"It's going to take some time for the spasm to let up," Carroll said. "If it doesn't, there are some considerations that we'll have to look at more seriously what's going on. We'll let him rest for a few days and see how it responds."
A year ago, Booty ran the first-team offense as Leinart recuperated from elbow surgery.
Kiffin said that in the seven-on-seven drills Tuesday, Booty completed 12 of 15 passes.
"John David was awesome" Kiffin said of practice Tuesday. "He was like a different guy. He was a bona fide, big-time quarterback by the way he walked, by the way he talked. It was a great day. It was a lot better than Matt Leinart's first day however many [three] years ago."
Booty appeared in 10 games last fall, completing 27 of 42 passes for 327 yards, three touchdowns and two interceptions.
"It's so frustrating for him," Carroll said. "He's been waiting for his chance. I feel terrible for him."
Sanchez, the 2004 Parade All-American Player of the Year, came to spring practice nearly every day a year ago, before he enrolled, to begin his preparation.
"Nobody has done more at this early stage of their career, has done more than Mark has done," quarterback coach Steve Sarkisian said Thursday. "He's able to function. We just need him to function at a little better pace. He's a little late on a couple of throws, but he's making very good decisions. He hasn't turned the ball over in two days. You guys know how our defense gets after the ball. He's making good decisions. We just need him to make them a little bit quicker."
Ivan Maisel is a senior writer at ESPN.com. He can be reached at email@example.com.