Castro was claimed by the Orioles on Saturday and optioned to Triple-A Norfolk.
Castro owns a 7.43 ERA in 13.1 innings of relief this season and a 6.00 ERA in 39 innings for his major-league career. If he earns a call-up at any point down the stretch, it will likely be in a low-leverage role. Phoenix Sanders was designated for assignment to clear space on the 40-man roster.