The 49ers signed Johnson to the practice squad Friday, Matt Barrows of The Athletic reports.
Johnson is expected to join the team at practice next week as long as he passes the COVID-19 protocols. The 34-year-old has spent time with 13 different NFL teams, but he only played games with five of those franchises, recording a 55.2 completion percentage and 6.1 yards per attempt over 33 games. Johnson played for the LA Wildcats of the XFL last spring, and he performed well with a 106.3 passer rating. He'll serve as the No. 3 quarterback in San Francisco because Jimmy Garoppolo (ankle) is out long term.