Riddick, who turned 30 on May 4, appeared in four games for the Raiders last season and also spent time on the team's practice squad. He was expected to be a pass-catching back out of the backfield but only caught five passes for 43 yards and ran the ball six times for 14 yards. He last played a full 16-game season in the NFL in 2017 for the Detroit Lions.
With both Riddick and Jalen Richard on the COVID list and Kenyan Drake on the Non-Football Injury list, the Raiders were thin with running backs at the start of training camp. But Drake returned to practice on Friday and the Raiders signed Darius Jackson and BJ Emmons the day before to join undrafted rookie Trey Ragas and Pro Bowler Josh Jacobs, who has rushed for at least 1,000 yards in each of his first two NFL seasons.