Frias, on the disabled list since July 1 with lower back tightness, will start Sunday after throwing a 31-pitch batting practice session.
Hatcher, acquired in the offseason Dee Gordon trade, has struggled (1-4, 6.38 ERA) most of the season in a setup role.
Frias, who stepped into the starting rotation after the injury to Brandon McCarthy, is 4-5 with a 4.54 ERA in 12 starts.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.