Felix Hernandez left the Seattle Mariners' opener in the fifth inning due to tightness in his groin.
The right-hander was removed before the sixth inning after throwing 65 pitches and allowing two solo home runs and five hits in a loss to the Houston Astros.
Hernandez might have suffered the injury while trying to cover first base in the fourth inning.
"It just got a little tight," Hernandez said. "I'll be all right. I'm going to be OK."
Making his 10th straight Opening Day start, Hernandez struck out six and took the loss in a 3-0 Mariners defeat.
Hernandez's next scheduled start is Saturday against the Angels. When asked if he thinks he'll be able to take his normal turn in the rotation, the 30-year-old said, "Oh yeah, for sure. I'll be there."