Johnson played for the Tampa Bay Buccaneers from 2008-11 before signing with the San Francisco 49ers this past offseason. He was released by San Francisco on August 31.
In 26 games (five starts) with the Bucs, Johnson completed 96-of-177 passes for 1,042 yards with five touchdowns and 10 interceptions.
Young is dealing with a thumb injury that likely will require surgery. He had 53 tackles, 1 1/2 sacks and three interceptions in 13 games this season.
In addition, the Browns signed defensive back Jordan Mabin to the practice squad.
