Brown (triceps) was in his seventh NFL season and was acquired via a trade with the Arizona Cardinals on October 2, 2013. He started Arizona's first four games this season but did not appear in a game with Pittsburgh.
Johnson (wrist) was in his fifth season with Pittsburgh and had appeared in all five games this season, making two starts and catching four passes. For his career, Johnson has appeared in 52 games, starting 26, and recording 22 receptions for 216 yards and one touchdown.
To fill the roster spots, the Steelers signed free agent tight end Richard Gordon and promoted cornerback Isaiah Green from the practice squad.