Baltimore optioned Walker to Triple-A Norfolk following Saturday's game against Washington.
Walker was called up from Norfolk last Monday and made three appearances for the Orioles, allowing two runs on three hits with a 5:2 K:BB over four innings. He threw 30 pitches Saturday, so Baltimore opted to send him back to the minors in favor of a fresh arm. Righty reliever Cameron Foster was recalled from Triple-A in a corresponding move.