ENGLEWOOD, Colo. — Joe Flacco will not be the Broncos’ quarterback on Sunday against the Cleveland Browns after the team discovered Denver’s starting quarterback has a herniated disc, Vic Fangio announced on Monday.

The injury, reported as a herniated disc, will keep Flacco sidelined for at least Sunday’s game and he will be re-evaluated after the team’s Week 10 bye week. However, it’s possible the injury ends Flacco’s season and the team places him on the injured reserve, although they will not make that decision immediately. At the moment, surgery is not believed to be needed, but “those things are fluid,” Fangio added on Monday.

Due to this, the Brandon Allen era has officially begun in the Mile High City as the 27-year old will make his first NFL start.

In fact, Sunday’s first offensive play for the Broncos will be Allen’s first career rep in a regular-season game. Not only has the 6-foot-2 quarterback never played a single snap in the NFL, he “hasn’t got a lot” of reps in practice since the team claimed him off waivers on Sept. 1.

“I can’t put a percentage on it, 15 percent, 20 percent of the practice plays,” Fangio said on Monday, guessing what percentage of the reps Allen has taken in practice up to this point. “But I do think—I’ve seen him a lot on the scout team and when he’s been in there a little bit on offense—I think the guy’s got a little something to him and we’ll devise a plan for him.”

Allen was a sixth-round pick in 2016 by the Jaguars out of Arkansas, where he was a three-year starter, throwing for 64 touchdowns to 26 interceptions. Allen spent his rookie season on the Jaguars active roster, although he never saw the field, before having the same role on the L.A. Rams the following year. He spent his third season on the Rams practice squad before Denver claimed him off waivers after the preseason.

“I think as comfortable as he can be given the lack of reps in practice,” Fangio said on Monday, explaining Allen’s comfort level in the Broncos’ offense. “The starter gets the bulk of the reps and he got here after preseason. There is some carryover to the offense that he came from to here, so that obviously helped.”

Denver’s starting quarterback has been decided, but the same cannot be said about the team’s now vacant backup spot.

With Drew Lock still on the injured reserve and Brett Rypien on the team’s practice squad, John Elway and Vic Fangio must make a move and activate one of them to the active roster. While many believe the decision is a no-brainer by activating the team’s second-round pick, the team is not as convinced.

“Well, we just have to decide too if Drew is ready because we may not even activate his two-week window and make a decision there because he hadn’t done anything in the huddle or the practice since what was it, the second or third preseason game when he got hurt. That’s a long time ago,” Fangio said, explaining why they may not activate Lock. “We want to make sure he’s ready before we put him out there.”

Lock is “pretty good” from a medical perspective after injuring his thumb in the preseason and Fangio believes “he’ll be fine.”

If the team does go with their talented second-round rookie, they will not consider starting him on Sunday.

Regardless of who the Broncos end up on as their backup quarterback, Denver’s quarterbacks on Sunday will have a total of zero career NFL reps.

With Tuesday’s trade deadline quickly approaching, Fangio doesn’t believe that will impact Denver’s quarterback situation moving forward.

Without Joe Flacco, Denver’s down to three unknowns at the most important position in sports. And who will be their backup quarterback remains a mystery.