Johnson signed a contract with the Lions on Saturday, Mike Garafolo of NFL Network reports.
It seems as if Tom Savage's potential concussion during Thursday's preseason opener may be worse than the Lions initially let on, as the team immediately set out to acquire a veteran backup for starter Matthew Stafford. Johnson underwent ankle surgery back in March but has been fully cleared to practice and should be healthy competition for Savage or David Fales as the trio competes for the No. 2 spot on the quarterback depth chart.