ENGLEWOOD, Colo. -- Denver Broncos quarterback Joe Flacco will miss Sunday's game against the Cleveland Browns with a herniated disk in his neck, and his season could be in jeopardy if the Broncos don't get a favorable medical report after the team's Nov. 10 bye.

Brandon Allen, claimed off waivers Sept. 1 from the Los Angeles Rams, will start against Cleveland. Broncos coach Vic Fangio said Monday the team will decide later this week if Brett Rypien will be signed and elevated to the roster from the practice squad, or if fellow rookie Drew Lock will be activated from injured reserve to be Allen's backup.

"Joe's not going to play this week. He's got a disk or neck injury," Fangio said. "He'll definitely miss this week and then we'll reevaluate after the bye and see where it's at."

During the second half of Sunday's 15-13 loss to the Indianapolis Colts, Flacco spent much of his time in between Denver's offensive series getting his neck attended to by the medical staff. After the game, Flacco said he first felt at least some neck pain "a couple weeks ago" and that "I don't know if I got hit on it [Sunday] or not."

Flacco was sacked three times by the Colts, including on the game's final play, and 11 times in the past two games. He has been sacked 26 times in eight starts this season. Only two quarterbacks have been sacked more often -- Cincinnati's Andy Dalton and Tampa Bay's Jameis Winston.

When asked whether Flacco would need surgery, Fangio said: "They don't know that yet. I think right at this minute they don't think, but those things are fluid."

Asked if Flacco could potentially move to injured reserve, Fangio said: "Not [as of Monday], but possibly, you know, we're still gathering the information."

The Broncos' struggles on offense have grown as the season has worn on. Denver is 22nd in total offense, 28th in scoring offense and 26th in passing offense, and has scored more than 16 points just once this season. The Broncos haven't scored more than 24 points since Week 7 of last season.

The three quarterbacks behind Flacco have not played a snap in an NFL regular-season game.

The Broncos claimed Allen off waivers after Lock suffered a right thumb injury during the preseason. They liked Allen's work in a similar scheme with the Rams, and he threw for 162 yards against the Broncos on Aug. 24 in the preseason in a little over a quarter or work.

"I think the guy has a little something to him and we'll devise a plan for him," Fangio said.

Although Fangio said Lock is essentially healed from the thumb injury, the rookie has not practiced in full-team drills since Aug. 17, two days before he suffered his injury against the San Francisco 49ers. Lock, who was selected with the 42nd pick of this past April's draft, has been on injured reserve since rosters were cut to 53 players just before the regular season began.

On Sunday, Flacco criticized Denver's conservative approach on offense, especially on a third-and-5 just after the two-minute warning with the Broncos clinging to a 13-12 lead. Running back Phillip Lindsay was stopped for no gain on the play, the Broncos punted and the Colts used a seven-play drive for Adam Vinatieri's 51-yard field goal to win.

"I just look at it like we're now a 2-6 football team and we're, like, afraid to go for it in a two-minute drill, you know?" Flacco said Sunday. "Who cares if you give the ball back with a minute [and] 40 seconds left? They've obviously got the field goal anyway."

Pushed on the Broncos' late-game offense, Flacco added: "Once again, we're a 2-6 football team and it just feels like we're kind of afraid to lose a game. It's third-and-5 at the end of a game; who care if they have a timeout at the end or not? Getting in field goal range isn't that tough. You're just putting your defense in these bad situations and I just felt like, what do we have to lose? Why can't we be aggressive in some of these situations? That's kind of how I feel a lot about the game today."

"He's just frustrated, like the rest of us," Fangio said Monday. "Upset and mad about the game, the way it went. I think he's talking about the whole fourth quarter, second half, when we struggled, not so much the last drive. ... I think his comments are more applicable to the whole second half."