Manager Don Kelly announced that Griffin (forearm) will begin a rehab assignment with Double-A Altoona on Tuesday, Colin Beazley of the Pittsburgh Post-Gazette reports.
The rookie shortstop has been rehabbing his forearm strain in Florida and has been cleared for game action after ramping up his throwing program over the past week. Per Dan Zangrilli of 93.7 The Fan, Griffin could return to the Pirates' active roster as soon as this weekend's series against the Reds.