The move comes one day after Castillo was taken to the emergency room after being hit in the groin by a foul ball in the team's loss to the New York Yankees.
Orioles manager Buck Showalter said Castillo has a "hematoma in his groin."
Castillo's situation is similar to that of teammate and fellow catcher Caleb Joseph, who was struck in the groin by a foul ball on the exact same day, May 30, last year. Showalter said Castillo's injury doesn't appear to be as severe.
To back up Joseph, the Orioles have called up catcher Francisco Pena from Triple-A Norfolk.
Information from ESPN's Eddie Matz was used in this report.