Gilbreath was optioned to Triple-A Albuquerque on Saturday.
Gilbreath was in the mix for an Opening Day roster spot during camp but has yet to pitch above High-A. As a result, he'll start the season at Triple-A Albuquerque but could be considered to make his major-league debut at some point in 2021. The southpaw made eight Cactus League appearances this year and posted a 7.36 ERA and 2.05 WHIP in 7.1 innings.