Allen, 25, has appeared in 21 regular season games, all with Baltimore from 2011 through 2012. The Bills signed him in January.
The Bills’ running back depth was solid even before the club added Philadelphia’s Bryce Brown this weekend. C.J. Spiller, Fred Jackson and Brown seem likely to be the club’s top three backs this season, with former Niners tailback Anthony Dixon also in the mix for playing time. All told, the Bills have five running backs on the roster, with first-year pro Ronnie Wingo rounding out the backfield.