The Mariners designated La Stella for assignment Tuesday, Sonja Chen of MLB.com reports.
The transaction clears a spot on the 40-man roster and 26-man active roster for right-hander Bryce Miller, whose contract was selected from Double-A Arkansas ahead of his MLB debut Tuesday versus the Athletics. La Stella began the season as Seattle's top designated hitter, but he hit just .190 with a .530 OPS and no home runs over 24 plate appearances. He could report to Triple-A Tacoma once he clears waivers, but La Stella has the right to refuse an assignment.