Mountcastle was removed from Friday's game against the White Sox due to right hamstring discomfort, Andy Kostka of TheBaltimoreBanner.com reports.
Mountcastle went 2-for-3 with a steal and a run scored prior to being replaced in the eighth inning, with Cooper Hummel entering in right field while Ryan O'Hearn shifted over to first base. Mountcastle will undergo further tests and the Orioles should provide an update on his injury during or shortly after Friday's contest.