The injury happened during Saturday's preseason game against the Washington Redskins. Gilmore left the game in the first half while the first team defense was still on the field and never returned.
Gilmore's injury came after Bills quarterback Kevin Kolb had already left the game after being unintentionally kneed in the back of the head on a scramble. The Buffalo News said Sunday concern in the organization for Kolb's long-term health is serious. The quarterback has already suffered at least three concussions in his seven-year career -- and depending on the severity of the most recent injury it could prompt Kolb to retire.
Kolb had been competing for the starting job with rookie signal-caller E.J. Manuel, who the team already said will miss at least the remainder of the preseason after undergoing minor knee surgery.
The injuries to Manuel and Kolb prompted the Bills to sign veteran free agent Matt Leinart and trade for Detroit Lions fourth-string quarterback Thad Lewis. The Bills sent third-year reserve linebacker Chris White to Detroit in the deal.
Both Lewis and White were considered long shots to make their respective rosters.
With Kolb out indefinitely and Manuel's status for the season opener unknown, the Bills are left with Leinart, a first-round pick gone bust who's spent parts of eight seasons mostly as a journeyman backup who was without a contract headed into this season, Lewis, and undrafted rookie Jeff Tuel out of Washington State.
Tuel has seen significant playing time due to the Manuel and Kolb injuries and has been productive at points -- though after entering the Redskins game failed to generate a single first down in the second half.
The injury to Gilmore, a second-year player Bills coaches hoped would have a breakout season after a successful rookie campaign, leaves a difficult hole to fill for Buffalo, the News said. Former cornerback Aaron Williams, who started most of last season opposite Gilmore, has been converted to safety. That leaves veteran Leodis McKelvin, who has failed to nail down a starting spot for much of his five seasons despite being a former first-round draft pick, as the top cover man on the roster when the Bills open their season Sept. 8 at home against the New England Patriots.