Head coach Sean McDermott confirmed after the game Allen is in the concussion protocol.
Let's check out how the injury could impact Buffalo's top playmakers in the fantasy football world.
Devin Singletary and Frank Gore
The Bills shook up their backfield following the preseason with the release of projected starting running back LeSean McCoy, who quickly landed with the Kansas City Chiefs.
Singletary, a third-round pick in the 2019 NFL draft, and Gore, a seemingly ageless legend, were thrust into the fantasy spotlight as a result. Although neither is expected to become a three-down workhorse this year, especially with T.J. Yeldon also in the mix, they each have upside.
Singletary missed Sunday's game with a hamstring injury. The Bills had listed him as questionable heading into the day, so it's reasonable to plan for a Week 5 return.
The Allen injury figures to benefit both rushers, albeit for different reasons.
Assuming he's available next week, Singletary will receive a boost in PPR formats because backup Matt Barkley is more likely to lean on checkdown passes than the big-armed Allen.
Gore should see more value in standard leagues since the Bills offense will probably become even more run-oriented while their second-year signal-caller is sidelined.
We're not talking about a game-changing role adjustment for either back, but it could net a couple extra points per game for the time being. Singletary could peak as a mid-range No. 2 fantasy rusher, while Gore could warrant consistent flex consideration.
Buffalo spent the offseason trying to better structure their offense around Allen, which meant finding a proven receiver with big-play ability. Brown was signed to fill that void.
While the the Bills offense as a whole isn't explosive enough to make him a must-start fantasy play, his potential for the occasional monster game makes him an intriguing No. 3 fantasy receiver. His floor would become much lower if Barkley started the next several games.
Since Buffalo would likely switch to an even more run-heavy, short-passing approach with its backup under center, Brown's boom-or-bust nature would likely land more often on the bust side.
Meanwhile, it would be an upgrade for slot target Cole Beasley and tight end Dawson Knox since they'll likely see an uptick in terms with Barkley leading the aerial attack.