According to Michael Sanserino, Grilli has already resumed his throwing program and could be back pitching in games by the first of September:
#Pirates closer Jason Grilli could start throwing off a slope or a mound as soon as early next week. Still on track for Sept. 1 activation.
Grilli’s return should place him firmly in the closer chair, which would move Melancon back to his setup role where he has thrived this season. The move would would reinforce an already strong bullpen.
The Pirates certainly want to get Grilli back into game shape prior to the playoffs, which would be the franchises first postseason appearance since 1992. Yes, you read that correctly.
At 72-49, Pittsburgh currently sits as the second best team in the National League (record wise), though, has division foes St. Louis Cardinals and Cincinnati Reds nipping at their heels, respectively 3 and 3.5 games behind.