Griffin (finger) will begin a rehab assignment at Double-A Altoona on Sunday, Colin Beazley of the Pittsburgh Post-Gazette reports.
Griffin has been out since early July due to a torn tendon in his left ring finger, but after ditching his splint and ramping up baseball activities over the past couple of weeks, he's now ready to test his finger in a competitive environment. He'll likely require a handful of minor-league games after spending such a long time on the sidelines, but he should be on track to return sometime in early September.