Casey will become the third Broncos starter who is expected to be lost for the season -- linebacker Von Miller and wide receiver Courtland Sutton are the others. And when he is formally moved to injured reserve in the coming days, Casey, a five-time Pro Bowl selection, will become the fourth Pro Bowl player on the team's IR list, joining Miller, Sutton and cornerback A.J. Bouye. Those players have been named to a combined 15 Pro Bowls.
Fangio believes he saw, when re-watching the game video Sunday night, when the injury happened in the second half.
"Like with a lot of injuries, they don't seem as bad (at first) as what they end up being and guys are able to finish (the game),'' Fangio said.
The Broncos have also been without quarterback Drew Lock (shoulder) and running back Phillip Lindsay (toe) and are now one of the league's four 0-3 teams after Sunday's 28-10 loss to the Tampa Bay Buccaneers.
Fangio was asked if the rash of injuries was uncharted ground for him as a coach.
"It probably is in light of the amount that you're talking about so early in the season,'' Fangio said. "Maybe in that regard it is. ... We've just got to keep moving on, next guy up will have to go in there and play good, the rest of the team will have to play good around everybody else.''
Casey, whom the Broncos acquired from the Tennessee Titans earlier this year for a seventh-round pick in the 2020 draft, is believed to have suffered the injury in the second half of Sunday's loss. Casey played 48 of the team's 68 defensive snaps in the game -- 71% -- which was just slightly lower than his snap count in the first two games combined (74%).
Casey finished the game with four tackles, a tackle for loss and a quarterback hit. The 10th-year veteran had an MRI Monday morning and the severity of the injury was confirmed.
Following Sunday's loss, Broncos coach Vic Fangio was asked about injuries in the game, and he mentioned only linebacker Austin Calitro, who had left the game with a hamstring injury.
The Broncos face the New York Jets Thursday night at MetLife Stadium.