Springboks wing Aphiwe Dyantyi faces a four-year ban, after confirmation of a positive drugs test for "multiple" banned substances, including an anabolic steroid.
The 25-year-old failed a drugs test in early July, but exercised his right to have the second sample tested.
On Friday, the South African Institute of Drug Free Sport confirmed that 'B' sample had also tested positive. Dyantyi denies taking any prohibited substance.
World Rugby's Breakthrough Player of the Year in 2018, Dyantyi has been provisionally suspended, until a hearing in front of an independent panel in about four weeks.
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Dyantyi has earned 13 international caps, but didn't make the cut for the Springboks' Rugby World Cup squad, after an injury-plagued season for Super Rugby's Lions. Coach Rassie Erasmus said the decision to omit Dyantyi was made before the results of his 'A' sample were released.
"SA Rugby, the Lions Rugby Company and Dyantyi are working with SAIDS,the World Anti-Doping Agency (WADA) and all other relevant authorities on the matter, and no further comment can be made at this stage," said the South African national body.
Dyantayi released a statement after his first failed test, proclaiming his innocence.
"I want to deny ever taking any prohibited substance - intentionally or negligently - to enhance my performance on the field," he said. "I believe in hard work and fairplay.
"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.
"Taking any prohibited substance would not only be irresponsible and something that I would never intentionally do, it would also be senseless and stupid."
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