The Athletics designated Bielak for assignment Saturday.
The move comes with the Athletics recalling right-hander Tyler Ferguson from Triple-A Las Vegas. Oakland acquired Bielak from the Houston on May 16 after the Astros DFA'd the 28-year-old right-hander May 11. Bielak appeared in three games for the Athletics, and he did not give up a run over his last two outings. He's out of minor-league options, but Bielak should still draw interest from teams that are in need of right-handed depth in the bullpen.