Frias initially was placed on the DL on July 5 with the same lower back tightness.
He started the season in Oklahoma City, so this was to be one of his option years regardless, but Frias will now earn his Major League salary while on the DL.
Frias last pitched in the Majors on June 30, but his rotation spot has been filled by newcomers Mat Latos and Alex Wood.
Steve Bourbon is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.