Seoul - South Korean Olympic swimming star and national icon Park Tae-Hwan fought to clear his name on Tuesday as he reeled from the shock news that he failed a doping test.

South Korea's Park Taehwan at the end of the fast heat of the men's 1500m freestyle swimming event during the Asian Games at the Munhak Park Tae-hwan Aquatics Centre in Incheon on September 26, 2014. [Photo/Agencies]

The four-time Olympic medallist blamed an injection given by a hospital for the result, the second high-profile Asian swimming case in recent months after China's Sun Yang.

Yonhap news agency quoted Park's management agency Team GMP as saying the 25-year-old dubbed "Marine Boy", who has an Asian Games pool bearing his name, was stunned by the news.

The report said the 25-year-old 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 Team GMP statement as saying late on Monday.

"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 has struggled to repeat the form of the 2008 Olympics, when he won freestyle gold and silver, and he was unable to win a title at his home Asian Games in September.