Detroit started the season with Jon Kitna, who has since gone to injured reserve with a back injury. The winless Lions have decided that second-year signal-caller Dennis Orlovsky needs guidance.
The 31-year-old Culpepper, a nine-year NFL veteran, had announced his retirement after the Oakland Raiders declined to re-sign him for the 2008 season. He has offered his services to any team needing a veteran backup, and had declined opportunities in Green Bay and Pittsburgh.
Other reports said he negotiated the deal without an agent and the Detroit Free Press said he would sign it Monday.
The former first-round draft pick by Minnesota in 1999 has compiled a 63.8 completion percentage, with 22,422 yards, 142 touchdowns and 94 interceptions in nine NFL seasons, including 2006 with the Miami Dolphins.