Motter was optioned to Triple-A Tacoma on Monday.
Motter made a start at first base over the weekend with Danny Valencia (wrist) sidelined, but he'll now head down to Tacoma in an attempt to get back on track at the plate. The 27-year-old hit just .206 in June and has earned only eight at-bats during the month of July. For the season, Motter is batting .204 with seven home runs and 23 RBI. A corresponding move is expected to be made later Monday.