Johnson was Dalton's backup in 2013, when he appeared in two games but didn't throw a pass. He signed with San Francisco last season and was inactive for each game. He left the 49ers as an unrestricted free agent.
Jason Campbell was Dalton's backup last season and became an unrestricted free agent. McCarron, a fifth-round draft pick, missed most of last season with a sore passing shoulder but was throwing without problem at the end of the year.
Johnson was Tampa Bay's fifth-round pick in 2008. He has also played for Cleveland.