A fourth-round draft pick by Detroit in 2010, Fox won the starting job at right tackle coming out of training camp last season.
But his time with the Lions was summed up when he sustained a groin injury in the opening game and missed the next three weeks.
In four years, Fox appeared in only 12 games, including three starts. A knee injury suffered in college at the University of Miami (Fla.) lingered into his rookie year in the NFL. Fox's progress also was slowed by a broken foot in 2011, along with other nagging injuries.
He was one of those players who it came down to availability more than ability.
Fox eventually became expendable for the Lions with the emergence of LaAdrian Waddle, an undrafted free agent who started eight games as a rookie.
The Lions' other top tackles are Riley Reiff and Corey Hilliard. The team will need to add another player to the mix either in the draft or through free agency.