Allen has been diagnosed with an injured ulnar collateral ligament in his right elbow, Adam Schefter of ESPN reports.
After suffering the injury Sunday at Houston, Allen was unable to return, and coach Sean McDermott eventually called him "week-to-week" Monday, per Chris Brown of the Bills' official site. While the injury isn't considered serious, an MRI of Allen's right elbow has been sent to Dr. James Andrews for a second opinion. For perspective, this injury cost Marcus Mariota two starts earlier this season, though he was pressed into action in the second one because his backup (Blaine Gabbert) suffered a concussion. In the aforementioned media session, McDermott said "all options are on the table at QB this week," so Nathan Peterman or even recent signee Derek Anderson may be under center Sunday at Indianapolis.