PROVO — One day after left tackle Matt Reynolds underwent surgery for a broken hand, the BYU offensive line was dealt an even bigger blow.

Starting left guard Jason Speredon sustained a torn rotator cuff during Thursday's practice, although the extent of the injury wasn't revealed until an MRI was performed Friday. Speredon, a junior, will undergo surgery and be out for the entire 2009 season.

"He has a high pain tolerance because he didn't act like it was that severe, but it was," coach Bronco Mendenhall said after Friday's evening practice. "We had a long chat in my office today. It was hard because he's had such a fantastic off-season and a really nice start to fall camp. He's having to do some adjusting right now. And our team is. I wish I could say it's not part of the game, but when it actually happens to each of us, it's difficult. We'll help him through it the best we can."

Speredon has played in 21 games over the past two seasons as a reserve.

Replacing Speredon in the lineup is walk-on Marco Thorson, a 6-foot-3, 307-pound redshirt freshman from Ramona High School in Ramona, Calif.

"He was kind of in the eighth spot coming into fall camp," Mendenhall said of Thorson. "He was actually playing really well. But with Matt Reynolds out for a while, and now Jason, it kind of changes."

Earlier this week, offensive line coach Mark Weber said about Thorson: "I feel really good about Marco Thorson. He's played every position this week on the line. He's tough. He gets it, football-wise. He has a good football IQ and can play the center and guard positions."

Thorson redshirted in 2005 before serving a mission to Rancagua, Chile. His nickname is "Moose," according to the BYU media guide.

Another redshirt freshman, Braden Hansen, is starting at left tackle in place of Reynolds until Reynolds returns from his hand surgery. He is expected to be out 2-3 weeks.

BYU head trainer Kevin Morris said Speredon was injured during a one-on-one drill.

"It's really a rare injury. On film, it didn't really look like that big of an injury. But it was. It's not (an injury) you see every day. ... All these linemen have sore shoulders this time of camp. He was more sore and more bruised (Friday) than he was (Thursday). He knew there was something going on. That's why we did the MRI this morning. But I wasn't expecting that injury. That was kind of surprising."

Speredon has a good chance at a full recovery, Morris said, adding that it takes about three months to recover from surgery, then a couple of months for rehabilitation.

Speredon has undergone five major surgeries during his career.