Upton grounded out in the first inning and came out of the game in the third.
"The trainers were afraid it was a hamstring," Upton said. "But it's not. After my first AB, I kind of got jammed and my foot stuck and I stumbled."
Manager Joe Maddon said Upton might be available off the bench Saturday. He's batting .258 with seven homers and 27 RBIs, and he has hit .326 with three homers in the past 12 games.