A lingering ankle injury led to the sudden retirement of Atlanta Falcons guard Hugh Thornton, a league source told ESPN.

The 25-year-old Thornton announced his retirement Tuesday afternoon. A former third-round draft pick of the Indianapolis Colts in 2013 out of Illinois, Thornton signed with the Falcons on March 21. He signed a one-year, non-guaranteed deal worth the NFL minimum of $690,000.

Thornton, who started 32 of 37 games in three seasons with the Colts, missed all of last season after having surgery on his ankle during training camp. The ankle did not respond like he wanted to once he joined the Falcons, according to the source.

This marks the second time an offensive guard has retired from the Falcons this offseason. Chris Chester, the starting right guard the last two seasons, retired after 11 NFL seasons.

Although Thornton had plenty of starting experience at right guard, he was never considered a legitimate contender for the starting role. The competition is destined to come down to second-year player Wes Schweitzer, fourth-year player Ben Garland, or perhaps rookie fourth-round draft pick Sean Harlow from Oregon State.

Harlow and fifth-round pick Damontae Kazee, a defensive back from San Diego State, both signed their rookie contracts Tuesday.