Grilli, 36, had been out for the last month and a half while dealing with a strained right forearm.
The Pirates have been using Mark Melancon in the ninth inning role lately but it should be just a matter of time before Grilli reclaims his role.
Prior to going down with the injury, Grilli recorded 30 saves, a 2.34 ERA and a 0.92 WHIP whle being selected as an NL All-Star.