Peavy originally was scheduled to toss Sunday, but the White Sox decided on moving the start to allow him an extra day of rest and recovery.
On Friday, Peavy was at U.S. Cellular Field, where he threw a rigorous bullpen session. Peavy said he experienced some back tightness in his last start, which was to be expected with a vigorous workload following a lengthy layoff.
"When you haven't started in two and a half months now, since May or so, you're going to have that soreness, especially when you're not easing into things," Peavy said. "It's not like I've been, 'Everybody's talking about Spring Training,' it's not like I've been prepared for that. It's just kind of jumping right back into it and trying to go at an awful high level, so certainly I think that soreness is to be expected. I certainly had quite a bit of that, but we're working through it."
Peavy has been recovering from a strained tendon in his right ankle, which he suffered while pitching for the Padres on June 13.
Peavy made his second Minor League rehab start Tuesday, against Tampa Bay's Triple-A affiliate in Durham, N.C., and lasted four innings, allowing four runs (three earned) on five hits. He hit one batter and walked none, tossing 44 of his 67 pitches for strikes. In his first Minor League appearance, he lasted three innings and threw 43 pitches.
He is 0-1 with a 3.86 ERA in seven innings of two rehab outings with 10 strikeouts and one walk.
Peavy said he expected to throw roughly 75 pitches in his third Minor League rehab start, with the hope that he could last five innings. He also said he would join the big league club in Boston after his Minor League start. Less certain, however, is when and where Peavy will make his next start.
Will he make a fourth Minor League appearance for Charlotte or a first Major League start for Chicago? Neither Peavy nor White Sox manager Ozzie Guillen was sure.
"We cannot rush him," Guillen said. "It's one thing about it with Peavy, a lot of people think this is Spring Training for him. No, because when Spring Training gets there, he prepared in the offseason to get to Spring Training. Right now, he couldn't do any thing for a few months.
"Definitely, we have to be careful about how we use him. We want it, but in the meanwhile, we're not desperate about it."
Jesse Temple is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.