Milwaukee Brewers starter Marco Estrada left Wednesday's game against the Giants after he injured his hip running the bases in the first inning.
Estrada grabbed his upper right leg as he rounded first base on a two-run double down the left field line, which gave the Brewers an early 6-0 lead against Barry Zito.
He labored into second, then came out of the game after being looked at by a trainer and manager Ron Roenicke.
The Brewers said Estrada had a strained right hip flexor and was set to have an MRI.
"When I saw the third baseman miss the ball I tried to push off and that's when I felt it pop," Estrada said.
Fellow starter Zack Greinke came in as a pinch runner and Manny Parra replaced Estrada on the mound in the top of the second.
Milwaukee won the game, 8-5.