LOS ANGELES — USC's beaten-up offensive line received a major boost yesterday when senior left guard Jeff Byers returned to practice.

Byers was able to participate in the non-contact morning session and some of the full-padded afternoon practice after doctors finally figured out what was causing him to have an enlarged spleen.

Byers contracted Rocky Mountain spotted fever, which is caused by tick bites, when he returned home to Fort Collins, Colo., earlier in the offseason to attend his sister's wedding. The ailment is treatable with antibiotics.

Byers underwent a battery of tests and even gave a bone marrow sample before finding out what was wrong Tuesday night. The news came as a relief.

"They tested him for all kinds of things," USC coach Pete Carroll said. "There were some days in there, waiting for results, when it was pretty tenuous."

"It's great news," Byers said. "We've still got to wait for the spleen to shrink a little more before they're going to really let me start going crazy, but today's a step in the right direction, no question."

Byers is the lone returning full-time starter on the offensive line, which has struggled without him, especially against blitzes. Carroll is ordering up more pressure packages than usual to get the offensive line up to speed as quickly as possible.

"You want to put them in as many stressful situations as they can handle and hope they get better at handling it," offensive line coach Pat Ruel said. "You can't practice it at half-speed. It's got to be full speed."

QUARTERBACK UPDATE

Offensive coordinator Steve Sarkisian classified the play of quarterbacks Aaron Corp and Mitch Mustain as "up and down" after reviewing the film of Tuesday's scrimmage and watching them practice Wednesday.

Both quarterbacks committed turnovers in Wednesday's morning session, which, like the scrimmage, ended with an interception. Corp and Mustain fared better late in the afternoon practice when they had time to throw. Mustain broke a tackle on the final play from scrimmage and raced into the end zone.

"I think they've done some really good things, and I think they've made mistakes," Sarkisian said.

"They're young guys, and they're going against a really good defense. What's critical is that we learn from the mistakes. Some of the mistakes we have learned from, some of them we've made twice now. We've got to learn from them so they don't make the same mistakes and continue to get better."

SANCHEZ PROGRESSES

USC quarterback Mark Sanchez was walking around the practice field Wednesday afternoon with a smaller brace that gives his injured left knee some degree of flexibility.

There's still no specific timetable for Sanchez's return from a dislocated kneecap, but Carroll viewed the change as an encouraging sign.

"I would think it's not going to take him very long" to come back, Carroll said. "Whatever the time frame that's normal, he's going to be at the early edge of that, easily."