Castillo spent time in the emergency room Tuesday night after being hurt in the ninth inning of an 8-3 loss to the New York Yankees.
The freak injury occurred when a pitch that hit New York’s Didi Gregorius ricocheted downward and struck Castillo between the legs.
Castillo is batting .317 with four homers and 17 RBIs.
Castillo was on the disabled list earlier this month with right shoulder tendinitis. Caleb Joseph received most of the starts behind the plate during that time.
Joseph started Wednesday night against New York. His backup was Fernando Pena, who had his contract selected by Baltimore from Triple-A Norfolk on Wednesday.