The A's reinstated left-hander Eric O'Flaherty from the disabled list and optioned right-hander Angel Castro to Triple-A Nashville on Tuesday.
O'Flaherty, who had been sidelined by a strained left shoulder since April 30, is 0-2 with a 11.57 ERA in eight relief appearances with the A's this season.
In a rehab assignment with Nashville and Class A Stockton, O'Flaherty did not allow an earned run, walk a batter or record a strikeout in two innings of work (two appearances).
Castro did not appear in a game during this stint with the A's, and he did not allow a run in three of his four relief appearances with Oakland.