Andy Pettitte left the New York Yankees' game against Seattle on Thursday night in the fifth inning after injuring a back muscle near his left shoulder.
Trailing 2-1, Pettitte struck out Kyle Seager for the second out of the fifth and reached for his right side with his left arm.
Yankees manager Joe Girardi went to the mound accompanied by pitching coach Larry Rothschild and a trainer. They spoke with the left-hander for a while, then Pettitte trotted to the dugout and was replaced by Shawn Kelley, a former Seattle pitcher.
New York said Pettitte hurt his trapezius muscle.
Pettitte allowed two runs, four hits and three walks in 4 2/3 innings with five strikeouts. He had been seeking his 250th big league win.