Peguero suffered a hamstring injury in Sunday's 19-6 win over the Rockies, Susan Slusser of the San Francisco Chronicle reports.
Peguero pitched one-third of an inning before sustaining the injury in the bottom of the eighth. The right-hander missed the entire first month of the season while recovering from a Grade 2 hamstring strain that he suffered during spring training, and he could be headed for another stint on the injured list.