World number 29 Dayana Yastremska says she is in "shock" after a provisional ban for failing a doping test.
The 20-year-old Ukrainian said she was told by the International Tennis Federation (ITF) she had tested positive for mesterolone metabolite, an anabolic agent, in an out-of-competition test in November.
"I firmly state that I have never used any performance enhancing drugs or any prohibited substances," she said.
Yastremska has won three WTA titles.
"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 said in a statement.
Yastremska, who has been ranked as high as 21 in the world, suggested the positive test was the result of a "contamination event".
"I am astonished and under shock, particularly given that two weeks prior to this test I tested negative at the WTA event in Linz," she said.
"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.
"Due to the confidentiality of the proceedings, you will understand that I am not able to share any further information at this stage. However, I am currently working with my team and you can be assured that I am resolutely determined to do everything to clear my name."
She was charged with an anti-doping violation on 22 December and the provisional suspension took effect on 7 January.
With no date announced for a hearing, her participation in the Australian Open is in doubt, with the season's opening Grand Slam beginning on 8 February.