Harrison hit a tiebreaking RBI single in the 11th inning but tweaked his ankle chasing down a looper to short left-center after moving from third base to shortstop to start the bottom of the inning.
Harrison landed awkwardly on the ankle and began hopping on his right foot, Singer reports, and later limped off the field.
The 27-year-old, who was an All-Star for the first time this season, initially injured his left ankle attempting to steal second against the Padres on Aug. 8, according to Singer, who added that "the joint has been tender ever since."
Harrison was not in the lineup for the Pirates' regularly scheduled game on Saturday. He is hitting .315 with 13 homers and 48 RBIs in 125 games this season, his fourth with the Pirates.
- Chris Mascaro