The six-foot-four, 316-pound offensive lineman made the stunning announcement in a release distributed by his agent, Dan Vertlieb.
Heenan, 26, had signed with the NFL's Indianapolis Colts following the 2015 season. He attended the Colts training camp and was injured but later rejoined the club's practice roster in November. Heenan was waived by the Colts Thursday morning.
Heenan, a native of Grand Coulee, Sask., was selected first overall in the 2012 CFL draft by the Saskatchewan Roughriders. He played three years with the club and was the starting right tackle on the Riders' Grey Cup-winning squad in 2013.
Heenan started 46 regular-season games with Saskatchewan before signing with the Colts in February 2015.
"My achievements in football simply would not have happened without the outstanding people I have had in my corner, and I will be forever grateful to everyone who helped me play the game for as long as I did,'' Heenan said in a statement. "I look forward to seeing what life has to offer after football.
(The Canadian Press)