On Monday, Peavy had an MRI that revealed swelling and strained muscles in his right elbow. He'll be placed on the 15-day disabled list Tuesday, a move made retroactive to Thursday.
Peavy will miss, at the minimum, two starts. He was scheduled to start Monday against the St. Louis Cardinals. His next turn in the rotation comes up on Saturday, and, just like Monday, left-hander Wil Ledezma will make that start.
The Padres will recall left-handed reliever Joe Thatcher from Triple-A Portland to take Peavy's place on the 25-man roster.
As for Peavy, he was equal parts reassured and frustrated by the turn of events, relieved that the damage wasn't worse and required surgery but unhappy that he had to go on the disabled list at a time when the struggling Padres (16-30) can't afford not to be at full strength.
"When you find out you're going on the DL, you're never happy," Peavy said after the Padres dropped an 8-2 decision to the Cardinals at PETCO Park. "You feel like you need to be out there in times like this."
Peavy had his MRI on Monday taken by team physicians. He'll have a third later in the week to see if the swelling in the elbow has subsided. Only after two or so weeks of no throwing -- and a clear diagnosis -- would he be allowed to begin throwing again.
The Padres, given their dismal start and the investment they've made in the 26-year-old (he signed a four-year, $52 million extension in December) the team will not push for a hasty return.
"You certainly don't like to lose your ace pitcher for any length of time," general manager Kevin Towers said. "But we're not going to rush him back. He's too important to this franchise, especially with the way things are now.
"We're not going to bring him back until he's 100 percent."
This isn't the first time Peavy, who is 4-3 with a 2.91 ERA in nine starts, has had issues with his pitching arm. Peavy missed five weeks in 2004 with a strained flexor in his right forearm. He did return to go 10-3 with a 2.18 ERA in 18 starts.
But Peavy said Monday that his injury in 2004 was located more toward the forearm and the swelling and strained muscles that have caused the soreness in his elbow for the past "three or four starts" are farther back in the arm.
"I don't think it's the same thing," Peavy said.
By his own guess, Peavy thinks that the last time he pitched without any pain in his right elbow was on April 27 against the Diamondbacks. He thinks he might have suffered the strain throwing on the side during a road trip in Philadelphia.
Peavy allowed four runs in four innings -- his shortest start of the year -- May 14 against the Cubs at Wrigley Field. Peavy said the elbow soreness was so bad that he felt it every pitch, and it occasionally left him without a full arsenal of pitches in any given game.
"Jake got to the point in his last couple of starts where he felt it was impacting his ability to make pitches," Padres manager Bud Black said. "When that happens, you have to take a step back, miss a start or two and then regroup. Let the muscles or whatever's causing the problem calm down, then go through the regimen to heal, get back on the mound."
The Padres first tried to treat the soreness internally with treatment, and also by having him skip his usual bullpen sessions between starts. But the pain wouldn't subside, not even after skipping throwing sessions or when he was doing things, like he said, in his everyday life.
"I think we made the right decision," Peavy said of going on the disabled list, though he lobbied for a cortisone shot if there was a chance that it would help get him back on the mound quicker. "We all wish we could do things differently where you would never get hurt. But that's not realistic."