Jake Peavy's up-and-down season took a downturn on Wednesday with the revelation that his next start will be pushed back because of arm trouble.
The right-hander was supposed to start Thursday against the Pirates, but Mark Buehrle will take his turn.
The White Sox then face phenom Stephen Strasburg and the Nationals on Friday, but Peavy might not make that start, either.
Although White Sox manager Ozzie Guillen told the Chicago Sun-Times that Peavy has a tired arm, The Associated Press characterized the injury as shoulder soreness. But the AP reported that an MRI showed no damage.
"We don't know, TBA," Guillen said, according to the newspaper. "We're going to give [Peavy] a couple more days. He has a couple more days off. His arm is a little tired, if you can put it that way. They call it a tired arm. Some call it a tired arm, some call it a dead arm. We'll go by ear [Thursday], see how he's doing."
Peavy, who informed the team of his discomfort on Wednesday, is 5-5 this season with a 5.62 ERA in 13 starts. He's trying to regain the form that made him the NL Cy Young winner for the Padres in 2007.
He's coming off a win over the Cubs on Friday. He's had a decision in 10 straight starts -- losing two and then winning three, losing two and then going win, loss, win.
Guillen said Peavy will be evaluated Thursday and possibly again on Friday to see when he can pitch again.
Information from The Associated Press was used in this report.