McKelvin was hurt in a 22-9 loss at Miami on Thursday. The seventh-year player had a team-leading four interceptions in nine starts this season. McKelvin also doubled as a return specialist.
The Bills filled McKelvin's roster spot by signing free agent defensive back Bacarri Rambo on Monday. Listed at 6-feet and 211 pounds, Rambo was selected by Washington in the sixth round of the 2013 draft.
He had two starts in 13 games with Washington before being released after Week 2 this season.
Buffalo also signed cornerback Brandon Smith to its practice squad.
The Bills (5-5) host the New York Jets (2-8) on Sunday.
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