Former New York Giants and USC cornerback
"I am proud of my accomplishments," Thomas, 30, told Giants.com. "I have been through a lot and I overcame it."
Thomas tore his anterior cruciate ligament three times, once at USC and twice with the Giants. He was sidelined for the 2005, 2011 and 2012 seasons.
Thomas played in all 16 games with the Giants in 2013 and became the second player in NFL history to play after three ACL surgeries.
A free agent in 2014, Thomas did not sign with a team because doctors would not approve his knee.
"When I realized the time was over, I always wanted to retire a Giant," said Thomas, who the team selected in the second round of the 2008 draft.
In six seasons and 60 games, Thomas had 12 interceptions.
At USC, Thomas had eight interceptions and 22 pass deflections. He was an All-Pac-10 second-team selection in 2007.