Tanner, a Dallas native who spent the past three seasons with the Cowboys, was recently released by the Indianapolis Colts.
The Cowboys need depth at running back for Thursday's preseason finale, in which starter DeMarco Murray and No. 2 back Lance Dunbar will rest as a precaution. Joseph Randle (oblique) and Ryan Williams (groin) are dealing with injuries.
The Cowboys will have to cut a player to make room for Tanner on the roster.