Sun Yang, one of the world's most-controversial Olympians, will have to overcome the biggest hurdle of his career after the World Anti-Doping Agency (WADA) elected to challenge a FINA decision to let the swimming champion walk free after he allegedly smashed a vial of blood with a hammer during a drug test.

Respected aquatic news website Swimvortex has reported that WADA didn't feel a warning was sufficient for Sun after the bizarre incident during a routine out-of-competition test at his home in China in November. Sun was alleged to have disputed the accreditation of one of nurses present and with the help of a security guard and his irate mother, went on to smash the vial of drawn blood with a hammer.

WADA will appeal FINA's decision on Sun Yang at the Court of Arbitration for Sport. Credit:AP

A FINA panel determined that the facts were too murky to make any ruling other than a series of warnings but WADA will now question that finding in front of the Court of Arbitration for Sport.

Should WADA win its case, Sun faces a lifetime ban from the sport, which would end a turbulent, dramatic and ultimately successful career that has seen him become the only man to win Olympic gold over 200m, 400m 1500m.