The 49ers plan to sign Johnson to their 53-man roster, Adam Schefter of ESPN reports.
Johnson has spent most of the year on the Broncos' practice squad, but the 49ers need help at quarterback after Jimmy Garoppolo sustained a season-ending foot injury Sunday. It seems likely that the 49ers will utilize Brock Purdy as their starting quarterback, but Johnson should provide a veteran presence in the locker room with the ability to fill in if Purdy struggles or gets hurt.