In order to make room for Thomas, the Cowboys announced they cut wide receiver Tim Benford. They have to make another roster move before adding Tanner.
With DeMarco Murray, Lance Dunbar and Joseph Randle (oblique) not playing against the Broncos and Ryan Williams bothered by cramping last week, the Cowboys only have D.J. Adams healthy and available at running back.
Thomas, who was cut by the New England Patriots, will allow the Cowboys to cover for the absences of Brandon Carr, Morris Claiborne (shoulder), Sterling Moore and B.W. Webb (hip flexor). Orlando Scandrick, who will be suspended the first four games of the season for violating the NFL's performance-enhancing drug policy, could play against the Broncos because he will no longer be allowed with the team starting Monday.
The Patriots drafted Thomas out of Georgia Tech in the sixth round last May. He can play corner and safety.