South Korean swimmer Park Tae-hwan has failed a doping test after receiving an injection that contained a banned substance.

The Seoul District Prosecutors’ Office said Tuesday that the Olympic medalist was found to have received an injection of Nebido, a testosterone enhancer, at a local hospital in July last year.

Testosterone is a substance banned by the World Anti-Doping Agency (WADA).

Officials at the hospital told prosecutors that they were unaware that the shot administered to Park to increase his testosterone levels contained a banned substance.

Park claimed that he repeatedly asked if it contained any illegal substances when he was offered the injection and that the doctor assured him there would be no problem.

Park’s agency said that he competed in the Incheon Asian Games two months after receiving the shot and was then notified that he failed a doping test.

The international governing body for swimming, FINA or Fédération Internationale de Natation, plans to hold a hearing on the matter late next month to decide the level of disciplinary action to take against Park .