ORCHARD PARK, N.Y. (AP) The Buffalo Bills' depth at running back could be further depleted after tests revealed rookie Karlos Williams sustained a concussion.

General manager Doug Whaley revealed Williams' injury Tuesday during his radio show on Buffalo's WGR-AM. Whaley says tests showed the concussion on Monday, a day after Williams complained of not feeling well following a 24-10 loss to the New York Giants.

Williams is following the NFL's concussion protocol, and must pass a series of tests before being cleared to play. Buffalo (2-2) plays at Tennessee (1-2) on Sunday.

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Williams was hurt after making his first start filling in for LeSean McCoy, who is out indefinitely because of a hamstring injury.

The Bills have only two other running backs on their roster, Boobie Dixon and Cierre Wood, plus fullback Jerome Felton.

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