Right-hander Sergio Mitre, who has been on the disabled list since June 15 and has not pitched since June 4, will start in Pettitte's place against the Kansas City Royals on Saturday.
Pettitte said he first felt pain after throwing a 2-1 slider to Kelly Shoppach. Manager Joe Girardi and trainer Gene Monahan went to the mound, and Pettitte threw one warmup pitch to catcher Jorge Posada as Girardi and Monahan looked on. The pitcher said he felt significant pain in his left groin during the follow-though of his delivery, and was replaced by reliever David Robertson.
"I've pitched through a lot of stuff, but there was no way. No way,'' said Pettitte, who at 38 is off to one of the best starts of his 16-year career. "Normally, I can pitch through anything but I was hurting pretty bad.''
Pettitte was taken to New York Presbyterian Hospital for an MRI, which revealed the Grade 1 strain, the mildest form of the injury. Considering Pettitte's age and history -- he suffered the same injury in 2001, missing 15 days -- the Yankees expect his recovery to take at least a month.
Pettitte said he can't remember the 2001 injury well enough to estimate the severity of Sunday's ailment. Pettitte pitches with a particularly long stride, and he said that, given his mechanics and his age, he would treat this injury with caution.
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"I stride way out and I have to make sure it's right," Pettitte said. "It's definitely something you want to be careful with. ... I'm not gonna try to rush it back. I'm going to try to get well."
In the meantime, Girardi said: "Someone is going to have to step up and take his turn.''
Mitre (0-1, 2.88 ERA) is a long reliever who made two emergency starts in May, once in place of Pettitte and once in place of Javier Vazquez. On May 10 in Detroit, he allowed four runs in 4 1/3 innings in a 5-4 loss to the Tigers, and on May 16, he held the Minnesota Twins to one run over five innings in a game the Yankees lost 6-3.
AP Photo/Bill KostrounTrainer Gene Monahan escorts Andy Pettitte off the field Sunday at Yankee Stadium.
"We're going to roll Mitre out there on Saturday,'' said Yankees general manager Brian Cashman. "He's been rehabbing well and he was a finalist for our fifth starter spot this spring.''
Pettitte's injury came one day after New York starter A.J. Burnett lasted only two-plus innings in a 10-5 loss, leaving the game with cuts on both hands following an angry fit in the clubhouse.
Frustrated by his ineffective outing, Burnett slammed open a set of double doors during the second inning Saturday, slicing both palms on the plastic lineup-card holders fastened to the entry. A day later, he said he apologized to his teammates for the outburst and will make his next scheduled start.
Wallace Matthews covers the Yankees. ESPNNewYork.com's Ian Begley and The Associated Press also contributed to this report.
Wallace Matthews has covered New York sports since 1983 as a reporter, columnist, radio host and TV commentator. He covers the Yankees for ESPNNewYork.com after working for Newsday, the New York Post, the New York Sun and ESPN New York 98.7 FM. Follow Wallace on Twitter »Chat archive »