O'Malley, who was competing for a utility job, was optioned to Triple-A Tacoma on Sunday, the Ryan Divish of the Seattle Times reports.
Luis Sardinas is the favorite to win the utility spot. O'Malley can play outfield, third base and second base, but he was weaker at shortstop, which the Mariners prioritized. He had a good spring, with 16 hits in 34 at-bats, six walks and four strikeouts. He'll likely be called up sometime this season when injuries hit.