Gallardo, 31, has struggled over 14 starts for the Mariners, compiling an ugly 6.30 ERA with a 57/32 K/BB ratio in 75 2/3 innings. The Mariners acquired him from the Orioles in exchange for outfielder Seth Smith back in January.
Moore, 23, is considered the Mariners’ No. 4 prospect according to MLB Pipeline. The Mariners selected him in the second round of the 2015 draft. This season with Double-A Arkansas and Triple-A Tacoma, Moore has posted an aggregate 2.72 ERA with a 77/17 K/BB ratio in 82 2/3 innings.