Peavy described a severe injury Wednesday, saying the muscle has apparently torn completely away from the bone. He said surgery is likely, and he could be gone for the season.
"We're going to see a couple doctors, and that's advised by our [team] doctors because our doctor simply hasn't seen a lot of this," Peavy said Wednesday. "He hasn't really seen this at all.
"I'm going to see Dr. [James] Andrews in Birmingham and consult with [Lewis] Yocum and get a lot of opinions to get the best way to handle this. Obviously surgery looks the way we probably have to go. And if that is, we'll just ride it. We did all we could do."
An MRI exam on Wednesday morning revealed the injury.
"It happens to a lot of teams," Sox manager Ozzie Guillen said. "We're not going to make any excuse, regardless of what happens from now until the end. It's not going to be an excuse about White Sox future. If we finish last, it's not because of Peavy. If we finish first, it's not because of Peavy.
"We still have a good ballclub. Whoever comes here, we are going to treat him as another starter. Hopefully, whoever comes in, just pitch the way he pitch and see what happens."
Jeff Marquez was called up from Triple-A Charlotte.
Peavy knew something was wrong immediately after throwing a pitch against the Angels on Tuesday night. Pain shot through his underarm and moved quickly down his back. He and the team's medical staff were hoping there would be even a minimal attachment of the muscles and ligaments before tests ruled it a complete separation.
"Obviously, I didn't want to say too much last night," he said Wednesday. "But I knew something was wrong when I walked off the field. I told you guys from the get-go, if you see me not taking the post or starting to walk off the field, like I did last night when it happened, you know obviously it's not good news."
Peavy wouldn't rule out a return just yet, but only because he hasn't talked to the experts.
"I can't say, just because we have no idea if there's a will and a way," he said. "I'd love to be back with this team being in contention. But like I said, I really don't know. We've just gone through our doctor, and our doctor doesn't have a clear-cut answer."
Peavy said he also felt discomfort in his June 30 start in Kansas City.
"I felt something in my last start," he said Tuesday. "We had something going on, some bruising in this area after my last start that we saw and treated.
"I saw the doctor and had a little strain in there that we treated. [I] played a little catch and knew I was going to feel it tonight and did a little bit. Obviously, I did more than feel it on that one pitch, and I knew I was done."
The White Sox considered skipping Peavy's turn in the rotation June 17 at Pittsburgh because of a sore right shoulder, but after an MRI exam showed no damage, Peavy insisted on pitching two days later against Washington. He fired a three-hitter against the Nationals for his fourth career shutout.
"I guess hindsight is 20/20," Peavy said Wednesday. "We certainly would have shut it down even before Pittsburgh.
"So, I don't think anybody made any bad choices here. We did all we thought we could do. I don't think anyone is at fault here -- myself for wanting to be out there or the team for letting me be out there. It's just part of sports. Sometimes stuff happens and when you pitch and play as long as I have, I was fortunate not to have an injury like this sooner. But it's happened, and we've got to make the best of it now. We're obviously going to weigh our options the next few days and make an educated decision and what's best."
Peavy has had numerous injuries to his arm, including a strained right forearm in 2004 and a strained right elbow in 2008. Both injuries landed him on the DL. Peavy missed three months in 2009 with a strained right ankle.
After a slow start to his season, Peavy has been a key part of the White Sox's resurgence. He had a 3-2 record with a 1.75 ERA in June. On the season, he is 7-6 with a 4.63 ERA.
Bruce Levine covers baseball for ESPNChicago.com and ESPN 1000. Jon Greenberg is a columnist for ESPNChicago.com. Information from The Associated Press was used in this report.