Williams had yet to play a game this season, as he held out the first eight weeks of the year. Upon his return after the trade deadline, he failed his physical due to discomfort with his helmet. Williams had a cancerous growth removed from his head during the offseason.
The roster move saves the Redskins from paying the remainder of Williams' $6-million salary, according to NFL Network's Ian Rapoport.
Williams has one year left on his contract. He sought a trade from Washington, but the team only began pursuing offers hours before the deadline.