The Royals recalled Hernandez from Triple-A Omaha on Saturday.
With Hunter Harvey on the injured list due to a back injury, Hernandez will return to Kansas City to fill the open spot in the Royals' bullpen. The 27-year-old righty owns a 3.86 ERA and 1.54 WHIP through 11.2 innings in the majors this year, though he has surrendered seven runs in just 7.2 frames since being optioned to Omaha in early July.