Garrett was optioned to Triple-A Jacksonville on Tuesday, Christina De Nicola of MLB.com reports.
Garrett was tagged for three runs on three hits and six walks over three-plus innings during Monday's start, and he'll return to the minors following the rough outing. The 24-year-old has struggled in eight outings for the Marlins this season with a 5.03 ERA, 1.82 WHIP and 32:20 K:BB across 34 innings.