Felix Hernandez left his Opening Day start for the Seattle Mariners in the fifth inning because of tightness in his groin.
Hernandez departed after throwing just 65 pitches, allowing two solo home runs and five hits in a loss to the Houston Astros.
"It just got a little tight," he said. "I'll be all right. I'm going to be OK."
The right-hander might have suffered the injury while trying to cover first base in the fourth inning.