Mike Klis of 9News first reported the move.
The ex-Detroit Lions running back also met with the New Orleans Saints and was choosing between the two. Riddick played under Broncos running backs coach Curtis Modkins in Detroit from 2013-15.
The Lions cut Riddick last month after six seasons. The 28-year-old is primarily a pass-catcher who struggles with efficiency as a runner. He compiled 288 carries for 1,023 rushing yards and five TDs. In the passing game, he's snagged 285 balls for 2,237 yards and 14 TDs. In his last season in Detroit, Riddick was used almost exclusively as a receiving back, so much so that defenses were essentially tipped off whenever he entered the game. He also struggled with efficiency and drops during the end of his run in Detroit.
In Denver, Riddick will be clearly behind Phillip Lindsay and Royce Freeman in the backfield pecking order. The signing puts into question Devontae Booker's role as the team's third-down back. We're likely to see a battle between Riddick and Booker this preseason to see who can earn the pass-catching reps out of the backfield.