South Korea's star swimmer Park Tae-Hwan failed a doping test, according to Yonhap news agency.

The Beijing Olympic men's 400m freestyle winner blamed an injection given by a hospital for the result, Yonhap reported Monday.

The report said Park was injected at a South Korean hospital while receiving chiropractic treatment before last year's Asiad in Incheon.

"At the time, the hospital offered to give Park an injection and he repeatedly asked if it contained any illegal substances," Yonhap quoted a statement from Team GMP, Park's management agency, as saying.

"The doctor said there would be no problem. And yet it turned out the injection contained a banned substance.

"He hasn't even taken cold medicine so that he wouldn't fail doping tests. Park is more shocked by this result than anyone else."

Park's agency threatened the hospital with legal action over the case, which could end in a ban for the swimmer with the world championships approaching in Kazan, Russia, in July.

Park won a gold and a silver at the 2008 Beijing Games to become the South Korea's first Olympic swimming medalist.

He also won silver in both events at the 2012 London Olympics, along with 400m gold in the world championships in 2007 and 2011.

But the 25-year-old only won a silver and five bronze medals at the Asiad last year.

Team GMP said Park passed doping controls during the Asian Games, but failed a recent World Anti-Doping Agency (WADA) test.

"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," the management agency said.