"Obviously this isn't good news," Peavy said Wednesday after having an MRI. "You know ... having something completely detached from the bone that's retracted down in my lat. Not good."
Peavy is 7-6 this season with a 4.63 ERA and 93 strike outs to 34 walks, but was finally starting to show signs of a true ace as he posted a 1.75 ERA in five starts through June.
The White Sox will certainly miss Peavy in the rotation, especially because it is unlikely the team explores trading for a pitcher.
In the meantime, Peavy has been placed on the 15-day disabled list.