Dayana Yastremska says she is "astonished" after the world number 29 was provisionally suspended for failing an out-of-competition doping test.
The International Tennis Federation (ITF) on Thursday revealed Yastremska was charged on December 22, having tested positive for mesterolone metabolite in a sample taken on November 24.
Ukrainian Yastremska, who reached a career-high 21st in the rankings 12 months ago, says she is not guilty of any wrongdoing and will do all in her powers to clear her name.
The 20-year-old posted on Twitter: "I firmly state that I have never used any performance-enhancing drugs or any prohibited substances.
"I am astonished and under shock, particularly given that two weeks prior to this test - on 9 November 2020 - 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.
"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.
"Besides, I have been informed that this substance is meant for use as medication by men and that women are advised not to use it due to the adverse effects it causes."
Yastremska said she was "resolutely determined to do everything to clear my name".
Rising star Yastremska has three WTA singles titles to her name.