Buffalo's best running back is out for the remainder of the Bills' game Sunday, and possibly longer.

Running back LeSean McCoy (ankle) was downgraded from questionable to out, per the team's official site, after suffering the injury early in the third quarter of the Bills' Week 17 game against the Miami Dolphins. McCoy pounded the ground in frustration while wincing as Bills trainers tended to him on the Hard Rock Stadium turf.

NFL Network's Mike Garafolo reported X-rays were negative and McCoy was diagnosed with a sprained ankle, according to a source informed of the situation.