The 24-year-old wing was named as World Rugby's breakthrough player of the year in 2018 but is now battling to save his reputation.

He has denied wrongdoing after the failed test which came after he attended a South African training camp last month, where he provided a urine sample to the South African Institute for Drug-Free Sport.

His B-sample will now be sent for analysis.

South Africa are due to name their squad for this year's Rugby World Cup in Japan today, although Dyantyi had already been ruled out with a reported hamstring injury.

"I want to deny ever taking any prohibited substance, intentionally or negligently, to enhance my performance on the field," said Dyantyi in a statement.

"I have never cheated and never will. 

"The presence of this prohibited substance in my body has come as a massive shock to me and together with my management team and experts appointed by them, we are doing everything we can to get to the source of this and to prove my innocence.

"As a professional sportsman on a national and international level, we get tested on a regular basis. 

"I have been tested before and again, since this test.

"Taking any prohibited substance would not only be irresponsible and something that I would never intentionally do, it would also be senseless and stupid."

Dyantyi plays for Johannesburg-based Super Rugby club side Lions and made his South Africa debut against England last year.

He has gone on to score six tries in 13 matches for the Springboks. 

"I want to apologise in advance to my team-mates and management at the Lions and Springboks, my friends and my family for the negative impact this news may have," he added.

"Personally, this game has given me an opportunity to inspire not only the young rugby hopefuls but South Africans across all walks of life and that is something I do not take for granted and something I would definitely not risk by doing a stupid act like this."