Gallegos was optioned to Triple-A Scranton/Wilkes-Barre following Tuesday's game against the Rays.
Gallegos was promoted from the RailRiders on Sunday but did not make an appearance during the brief stint in the majors. The 26-year-old returns to Scranton/Wilkes-Barre, where he has a 3.55 ERA and 1.11 WHIP over 25.1 innings this season.