The Japanese short track speed skater Kei Saito has protested his innocence after becoming the first athlete at the Winter Olympics to be suspended for a positive drugs test.

The news was announced by the Court of Arbitration for Sport, who said that the 21-year-old voluntarily accepted a provisional suspension after an out-of-competition test showed signs of acetalozamide, which can be a masking agent and is used as a diuretic.

The revelation will be a major embarrassment to Japanese sports, which prides itself on its clean image and will be hosting the 2020 Summer Olympics in Tokyo.

However Saito, who had been due to compete in the second heat of the men’s 5,000m relay on Wednesday, vowed to “fight” any potential sanction after leaving the Olympic village.

At a press conference Japanese officials said that Saito maintains there is no way the substance could have entered his body after he passed the test on 29 January.

Hidehito Ito, the deputy chef de mission of the Japanese Olympic Committee, told reporters: “He has decided not to place any further burden on his fellow Japanese athletes and that is why he has left the village.

“We will do everything in our power to help him. We will give him every help he needs.”

Tsutomu Kawasaki, Japan’s short track speed skating head coach, added: “Obviously we are surprised and it is a disappointment for the team.”