Dayana Yastremska, the world number 29 in the women’s tennis rankings has been provisionally suspended after a banned substance, mesterolone, was found in an out-of-competition sample.
Ukrainian Yastremska, whose highest ranking was 21 a year ago, said in a statement she was "astonished" and "under shock" after the positive test for the banned substance.
A positive test for mesterolone carries a mandatory provisional suspension, which came into force today.
Yastremska tested positive on November 24 2020 and was charged with an anti-doping rule violation by the International Tennis Federation on December 22.
In a statement on social media Yastremska said: "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 November 9 2020 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.
"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.
"I am currently working with my team and you can be assured that I am resolutely determined to do everything to clear my name."
Yastremska has the right to apply to the Chair of the Independent Tribunal to hear a case as to why the provisional suspension should not be imposed, but has chosen not to exercise that right to date.
The 20-year-old has won three Women’s Tennis Association tournaments in her career – at Hong Kong in 2018 and at Hua Hin and Strasbourg in 2019.