Pettitte revealed that he thought he strained his back while working out between starts at Rangers Ballpark in Arlington, forcing him to skip his usual bullpen session between starts. Pettitte worked into the sixth inning before being lifted in the Yanks' 3-1 victory over the Indians.
"I guess it's a little bit of old age," Pettitte said. "That's all I can tell you. I literally wasn't doing anything. I felt great working out, I lifted my legs and it was just one of those freak accidents."
Pettitte said the Yankees were aware of the injury, which he first felt while jogging in the outfield on Monday and said was exacerbated on Friday by several slips on a soft mound at Progressive Field.
Pettitte first bent over with some stiffness in the fourth inning, drawing Yankees manager Joe Girardi and assistant trainer Steve Donohue onto the field, but told them he could continue and recorded six more outs while getting heat treatment between innings.
"I think slipping a couple of times might have just flared me up a little bit," Pettitte said.
The Indians threatened in the sixth, and Girardi said he saw Pettitte unable to finish his pitches. Mark DeRosa singled and Ben Francisco walked on four pitches, drawing Girardi out for a conference before Pettitte threw two more balls to Jamey Carroll.
That brought Girardi and Donohue back out, and though Pettitte protested, his evening was complete after 84 pitches. Girardi said he was worried about Pettitte overstriding and potentially hurting his pitching arm.
"We knew about it early in the game, but he said he was OK," Girardi said. "I just decided from what I saw, I didn't like it, and it was hard. He was trying to grit it out, and that's what Andy always does."
Alfredo Aceves relieved Pettitte, who logged the victory to improve to 5-1 this season with a 4.10 ERA. In hindsight, Pettitte said it may have been a good idea to give the game to the relievers.
"It was probably smart," Pettitte said. "I was feeling some pressure when I would land for a few innings. It was probably the best thing to do."
Girardi said that he believes Pettitte will make his next start, which would come Wednesday against the Rangers in New York, but it is not a certainty. Should Pettitte be unable to start, Chien-Ming Wang could be tabbed to return to the rotation from his bullpen assignment.
"We've got to try to knock this out," Girardi said. "Hopefully it doesn't linger, because the longer it lingers, the less work [Pettitte] can do and be prepared for his next start."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.