SEOUL (Yonhap) — South Korean Olympic swimming champ Park Tae-hwan has failed a doping test, his agency said on Monday, blaming the result on an illegal injection administered by a local doctor.

Team GMP, the swimmer’s agency, confirmed an earlier report that the 25-year-old tested positive in a recent World Anti-Doping Agency (WADA) test. In a statement, the agency claimed that a South Korean doctor gave him an injection that unbeknownst to Park contained a banned substance.

“As a world class swimmer, Park Tae-hwan has been extremely careful about what he takes, and he hasn’t even taken cold medicine so that he wouldn’t fail doping tests,” the statement read. “Park is more shocked by this result than anyone else.”

Park competed at the Asian Games in the South Korean city of Incheon last September and passed multiple doping tests during the event, Team GMP said.

The agency said Park received free chiropractic treatment at a local hospital about two months prior to the Asian Games, and received a shot that led to the positive test.

“At the time, the hospital offered to give Park an injection and he repeatedly asked if it contained any illegal substances,” the statement said. “The doctor said there would be no problem. And yet it turned out the injection contained a banned substance. With our team of legal experts, we’re trying to determine why the particular hospital injected Park with an illegal substance, and we’re preparing to hold it civilly and criminally liable.”

Team GMP added that it believed giving a well-known athlete an illegal injection ahead of a major event “clearly constitutes an unlawful act.”

Park became the first South Korean to win an Olympic swimming gold when he took the men’s 400-meter freestyle race at the 2008 Beijing Olympics. He added a silver in the 200ｍ freestyle.

He grabbed two silver medals at the 2012 London Olympics in the 200ｍ and the 400ｍ freestyle events. He has also won two world championships in the 400ｍ freestyle.

Park is the most decorated South Korean in Asian Games history with 20 medals, including six gold medals.