SEATTLE -- First it was John Danks, starting the 2013 season on the disabled list as he built up strength in his throwing arm that underwent season-ending arthroscopic shoulder surgery last Aug. 6.
Then, it was Gavin Floyd, who had his own season-ending Tommy John surgery on May 7 to repair a damaged ulnar collateral ligament and a torn flexor muscle in his right elbow.
Even Chris Sale missed one start because of a mild case of tendinitis in the back of his left shoulder.
The current season has not been very kind to the White Sox rotation, and fortunes took another turn in the wrong direction Wednesday afternoon.
Jake Peavy's MRI revealed a non-displaced rib fracture on his left side. He will be shut down for four-to-six weeks, and the only treatment for him is rest.
Peavy exited in the third inning of Tuesday's 7-4 loss to the Mariners because of the pain, which hampered the right-hander when he was on the mound and limited his fastball to a top velocity of 90 mph.
X-rays taken at Safeco Field proved negative for a fracture, but the MRI showed differently.
"It's just unfortunate. It's unfortunate that something crazy like this comes about," said Peavy, following Wednesday's 7-5 White Sox victory in 16 innings. "The hardest thing is there is nothing to do to help a bone heal quicker.
"You don't cast it. You feel normal, but yet you can't even ride a bike. When you are hurt, you go to the training room and feel like you are being productive. Something like this, you have to let things heal. It's tough."
With the right-hander out of action for an extended period, White Sox manager Robin Ventura said that Hector Santiago would move back into the rotation Sunday afternoon against the A's. Pitching coach Don Cooper confirmed that fact, but it's not known for certain if Santiago will keep that role during Peavy's entire absence.
"They kind of gave me a heads-up when they told me I was going back to the bullpen," Santiago said. "'If a guy could use a spot start, you will be the guy. We won't bring anybody up.' I'm mentally ready for it."
Santiago threw just one-third of an inning and only 12 pitches in relief Tuesday night, admitting that he was somewhat surprised not to be the first guy up when Peavy departed. Santiago threw another two-thirds of an inning and just nine pitches on Wednesday.
This pain started for Peavy on Sunday in Oakland, but the veteran added there might have been something there previously that would account, in part, for his similar velocity dip against the Cubs last Thursday at Wrigley that had his fastball topping out at 90 mph. He couldn't put a finger on the cause, adding that having his back realigned or cracked by Adam Dunn or Mark Parent for what he thought was a rib being out of place didn't help matters.
Neither did pitching on Tuesday.
"Obviously, last night trying to go through it caused a little more edema and blood to the area and it may take a little bit more time because we tried to push through it," Peavy said. "I wanted to be out there last night and give a better effort. I just wasn't able to. But you can't look back and you can't live in the past."
"I can't sit there and figure out the guy unless he gives you the information. He felt he could get through it," said Ventura. "It's one of those where he started out and looked all right. By the time he got to the third, it looked like there was something going on."
After agreeing to a two-year, $29 million deal with the White Sox before reaching free agency this past offseason, Peavy went through Spring Training perfectly healthy. He missed a May 2 start in Arlington, Texas, because of lower back pain, replaced at the time by Santiago.
Missing six weeks takes Peavy out of trade consideration, if general manager Rick Hahn decided to move what would have been one of his more marketable pieces before the July 31 non-waiver Trade Deadline.
It would be career start No. 10 for Santiago on Sunday and his sixth start of 2013, giving the southpaw a chance to break a small stretch of two rough career relief outings against the A's in Oakland.
"That will be a different shot, starting instead of pitching the 9th or 10th," Santiago said. "But I definitely want to get back out there against them. I'm 0-for-2 against them with two walk-offs."