The Giants recalled Hjelle from Triple-A Sacramento on Monday, Maria I. Guardado of MLB.com reports.
With the placement of Scott Alexander (hamstring) on the 15-day injured list Monday, Hjelle will be called on to replace Alexander in the bullpen. The 26-year-old righty holds a 10.13 ERA and 2.33 WHIP through 13.1 innings in the majors this season, and he's been used exclusively out of the bullpen with the Giants despite serving as a starter in Triple-A.