Klein suffered a back injury Wednesday and will not practice Thursday, Chris Brown of the Bills' official site reports.
The veteran barely sees the field on defense these days, but he's still a strong special-teams player at 32 years of age and saw action on 54 percent of the special-teams snaps in last Thursday's win over Tampa Bay. The Bills don't have much depth at linebacker following a major injury to Matt Milano (leg) in Week 5, so they might have to promote someone from the practice squad if Klein can't play Sunday night in Cincinnati.