Stallings (neck) will begin a minor-league rehab assignment with Triple-A Indianapolis on Saturday, John Perrotto of DKPittsburghSports.com reports.
Stallings is dealing with a cervical neck strain. It's not clear when he's expected to return, but he won't have a major-league roster spot to come back to, as Elias Diaz is back as the backup catcher after missing an extended period due to illness.