Chubb was injured in the Broncos' 26-24 loss to Jacksonville on Sunday although he finished the game and forced a fumble on the last series. The ball bounced right back to quarterback Gardner Minshew, who then drove the Jaguars for the game-winning field goal as time expired.
Chubb had 12½ sacks last season and one on Sunday. In the locker room afterward, Chubb said his knee was fine. Coach Vic Fangio said Chubb awoke Monday in pain and went for an MRI and was surprised at the seriousness of his injury.
The Broncos' 0-4 start matches their worst in their history. They face the AFC West rival Los Angeles Chargers on Sunday.