Ukraine's Dayana Yastremska has been provisionally suspended after the World Anti-Doping Agency (WADA) found a banned substance in an out-of-competition urine sample.
Yastremska, 20, provided the sample in November and a WADA lab in Montreal found the presence of mesterolone metabolite, an anabolic agent on its Prohibited List.
"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 International Tennis Federation says.
"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."
Yastremska, the world No,29, denies 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 practicing 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 a contamination event."
The ITF did not say when Yastremska's hearing would take place, putting her participation in the February 8-21 Australian Open in doubt.