Harrison suffered the injury late in the opening period of Sunday's game, after Pittsburgh Steelers wide receiver Cedrick Wilson was taken down from behind and rolled on the All-Pro safety's leg.
Harrison underwent an MRI Monday that revealed the extent of the injury.
The NFL's all-time sack leader by a defensive back, Harrison, 32, was a key player during last season's win over Pittsburgh in the AFC Championship game as he returned an interception for an 87-yard touchdown.
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