Pittsburgh originally placed Grilli on the disabled list on July 23 with a right forearm strain. Grilli had been on a rehab stint with Double-A Altoona, where he threw two scoreless innings and struck out four batters.
Grilli will not immediately resume ninth-inning duties for Pittsburgh. Instead, Mark Melancon will remain in the role for the time being. Grilli has a 2.34 ERA over 45 games in 2013, and has saved 30 games for the Pirates. Melancon is in the middle of a fantastic season, with just a 0.88 ERA and 0.85 WHIP in 62 appearances.
With the Pirates holding just a 1.5-game lead in the National League Central, the team appears to want to go with the hot hand until they are sure that Grilli is back to his old form and fully over his injury.
Pittsburgh made a handful of other moves on Tuesday, calling up RHP Jared Hughes, OF Andrew Lambo, C Tony Sanchez and LHP Jeff Locke from the minors. With rosters expanded in September, the Pirates do not need to demote any players to make room for the call-ups.
Locke is the big name of the four. A first-time All-Star in 2013, Locke has struggled over the last month-and-a-half with an 8.10 ERA in his last six starts. Despite that, Locke still has just a 3.22 ERA on the year. The Pirates sent him to Double-A Altoona as a way to give him some rest without occupying a roster spot.
The Pirates have Locke scheduled to start on Saturday for the first time since Aug. 27. It will be a big game for the Pirates, who will play the St. Louis Cardinals in a game that will help decide which team wins the division.