Colts head coach Frank Reich told reporters Leonard won't suit up against the Falcons due to a concussion. He started feeling concussion-like symptoms after Sunday's game against the Tennessee Titans, and has since been placed in the league's concussion protocol, according to the team.
"Everyone will just step up in their role, and I'd rather not get into the details of what that'll look like," Reich said. "But everyone will just step up and we've had a good week of practice. Those guys are ready to go."
Leonard, who led the NFL in tackles (163) as a rookie last season, didn't come close to passing the league's concussion protocol, as he missed the entire week of practice.
Sunday will mark only the second game that Leonard has missed. He sat out of the Colts' Week 5 matchup against the New England Patriots in 2018.
In two games this season, Leonard leads the team in total tackles (18) and has one sack and a pass breakup.
Rookie Bobby Okereke and E.J. Speed could take Leonard's reps in his absence Sunday. Anthony Walker, who typically starts in the middle, could move to the outside with Leonard out.