Ridley was one of six running backs on the depth chart and signed a one-year deal with $250,000 guaranteed after spending last season with the New York Jets.
The move could signal the return of starter Ameer Abdullah. After surgery on his shoulder in January, Abdullah has been limited in workouts and began practicing with a non-contact jersey.
Theo Riddick nailed down the third-down back role last season and the Lions are pleased with rookie seventh-round pick Dwayne Washington. Washington helped his cause with a 96-yard kickoff return for a touchdown against the Steelers.
Ridley could draw interest from the New England Patriots, his first NFL team, because of injury woes in their backfield. Dion Lewis underwent knee surgery and the Patriots parted with Donald Brown because of durability issues.