The Diamondbacks optioned Frias to Triple-A Reno on Monday.
Frias' move to Triple-A clears a spot on the 28-man active roster for right-hander Ryne Nelson, who was called up from Reno in advance of his scheduled start Monday agains the Padres. Following his promotion from Triple-A on Aug. 21, Frias made six appearances out of the bullpen and allowed seven earned runs on six hits and two walks across 5.2 innings.