Frelick left the second game of Saturday's doubleheader against the Royals with left side tightness.
Frelick singled in the top of the fourth inning but then left the game after a visit from the training staff. The Brewers have since clarified that it's a left side issue, though the severity of the injury remains unknown. Brandon Lockridge replaced Frelick in the game and could see more at-bats if Frelick is forced to miss additional time.