The body of Lee Gyeong-hwan, 24, was found outside an apartment building in central Incheon, west of Seoul, at the weekend, Yonhap news agency quoted local police as saying.
Lee was booted out of the K-League after a sting into allegations of match-fixing last year, which prompted the South Korean government to threaten to shut down the league.
The game's image was left battered following the probe, which led to nearly 50 players being arrested.
It was the worst scandal to hit the K-League in its 29 years, with a former coach and another former player also found dead after suspected suicides.
The K-League Cup competition was scrapped as part of sweeping measures implemented to clamp down on corruption following the government's threat of closure.
Soccer was not the only South Korean sport tarnished by match-fixing allegations, with arrests made and bans dished out in volleyball, baseball and even power boat racing.