INDIANAPOLIS -- Colts All-Pro linebacker Darius Leonard has been ruled out for Sunday's game against the Atlanta Falcons due to a concussion, coach Frank Reich said Friday.

Leonard, who led the NFL in tackles (163) as a rookie in 2018, suffered his concussion in last weekend's victory at Tennessee. He didn't come close to passing the NFL's concussion protocol because he missed the entire week of practice.

Sunday will mark just the second game that Leonard has missed. He missed the Week 5 game at New England last season. Leonard leads the Colts in tackles with 18.

Rookie Bobby Okereke will likely start at middle linebacker, with Anthony Walker, who normally starts in the middle, expected to move to the outside with Leonard out.

"[Okereke looks] like he needs more playing time. He's that kind of guy," Reich said. "... He'll get some more time this week."