Ukraine's Dayana Yastremska, a top-30 player who had been expected to compete at next month's Australian Open, has been provisionally suspended after the World Anti-Doping Agency (WADA) found a banned substance in an out-of-competition urine sample.
The International Tennis Federation (ITF) reported on Thursday that the rising 20-year-old had provided the sample in November but Yastremska denies any wrongdoing, saying she was "shocked" at the news.
The ITF said a WADA lab in Montreal found the presence of mesterolone metabolite, an anabolic agent on its prohibited list, in her sample.
"Yastremska was charged with an Anti-Doping Rule Violation under Article 2.1 of the Programme (presence of a Prohibited Substance in a Player's Sample) and was provisionally suspended with effect from January 7," the ITF said.
"Yastremska had (and retains) the right to apply to the Chair of the Independent Tribunal convened to hear her case why the Provisional Suspension should not be imposed, but has chosen not to exercise that right to date."
The ITF did not say when Yastremska's hearing would take place, putting her participation in the Australian Open between February 8 and 21 in doubt.
She has twice competed in the Melbourne Grand Slam main draw before, reaching the third round in 2019 and the second round last year.
Yastremska, ranked 29 in the world, denied having used performance enhancing drugs and believes the positive test was the result of a "contamination event".
"I'm astonished and under shock, particularly given that two weeks prior to this test... I tested negative at the WTA event in Linz. After this last tournament of the year, I stopped practising to rest prior to the start of the new season," she said in a statement.
"Only a very low concentration of mesterolone metabolite was detected in my urine. Given that low concentration and given my negative test two weeks earlier, I have received scientific advice that the result is consistent with some form of contamination event."