The Japanese star was given a four-year suspension by the International Swimming Federation (FINA) in October of last year after he tested positive for anabolic agents ostarine and ligandrol.

Koga, a former world champion in the 50 and 100 metres backstroke, appealed the decision from FINA to the CAS after arguing dietary supplements were the reason for his failed test.

In a statement, the CAS revealed the parties involved "informed the CAS that having agreed that contaminated supplements were the most likely source, on a balance of probability, of both the ostarine and ligandrol found in Junya Koga’s samples".

The CAS added that a settlement agreement, shortening Koga's ban to two years, had been reached.

His ban has been backdated to May 15, the date he was provisionally suspended, and he will be free to return to competition on May 14 next year.

It is unlikely the 32-year-old, who represented Japan at Rio 2016, will be able to compete at the Olympic Games in Tokyo, which begin are due to begin on July 24, as the Japanese Olympic trials are set to be held in April.

Koga, a three-time Asian Games gold medallist, was withdrawn from the Japanese team for Jakarta Palembang 2018 after news of his positive test emerged.

Both substances can help build muscles and are listed in the World Anti-Doping Agency prohibited list as "other anabolic agents".

Ligandrol is also the substance Australian Commonwealth Games gold medallist Shayna Jack tested positive for.

Jack, who is facing a four-year ban, has denied intentionally doping.