The A's designated closer Jim Johnson for assignment, the club announced Thursday morning.
Oakland acquired Johnson in December in exchange for Jemile Weeks and minor league catcher/first baseman David Freitas.
In 38 games for the A's this season Johnson went 4-2 with a 6.92 ERA.
On Wednesday night, Johnson entered the A's game against Houston with a 9-2 lead. He allowed four straight hits -- single, single, double, single -- and was relieved before recording an out.
Oakland recalled Evan Scribner from Triple-A Sacramento to fill Johnson's roster spot.