Miller tore the anterior cruciate ligament in his right knee in the first quarter of Sunday's victory over Houston on a non-contact play.
Broncos Coach John Fox said Monday a magnetic resonance imaging exam revealed the extent of the injury.
Miller is a key element of the Super Bowl contenders' defense, racking up 34 tackles and five sacks over eight games this season.
He missed six earlier games while on suspension for violating the NFL's substance abuse policy.
Linebacker Brandon Marshall was tapped from the practice squad to fill Miller's roster spot.