Bates (groin) was placed on IR on Thursday, Tori McElhaney of the Falcons' official site reports.
Bates had already been ruled out of the team's Week 11 matchup with the Patriots, but he will now miss a minimum of two additional games on top of that. With the Falcons' Week 12 bye also falling during that stretch, the earliest the backup linebacker can return will be Week 15 against the Panthers.