The 28-year-old Barkley, in his sixth season out of USC, played in all four preseason games for the Bengals. However, he sustained a left knee injury in the preseason finale vs. Indianapolis and was placed on Reserve/Injured on Sept. 1 during final roster cuts.
The Bengals signed Barkley to a two-year contract in March, and had he remained on Injured Reserve he would have been eligible to compete for a spot with the team next season.
Andy Dalton is the Bengals' starting quarterback, with Jeff Driskel as his backup and Christian Hackenberg on the practice squad. It is believed Barkley would have been the backup had he not been injured.
When he is healthy, Barkley is free to sign with another team.
The 6-2, 227-pound Barkley was expected to be a first-round pick in the 2013, but his stock dropped after a shoulder injury sustained in his senior year at USC.
The Philadelphia Eagles selected him in the fourth round (No. 98 overall) and he spent two seasons with the Eagles and parts of others with the Arizona Cardinals (twice), Chicago Bears, San Francisco 49ers and the Bengals.
Barkley has played in only 13 NFL games, four in his two seasons with the Eagles, and made his only six starts while appearing in seven games for the Bears in 2016.
His career statistics are 159 completions in 266 passes for 1,911 yards, with eight touchdowns, 18 interceptions, with 63.7 quarterback rating.