World No 29 Dayana Yastremska has tested positive for a banned substance.

The 20 year-old from Ukraine has since been provisionally suspended, the International Tennis Federation announced, following an out-of-competition doping test.

Yastremska tested positive for a substance that can be used to boost testosterone following a urine sample on November 24, but the rising star said in a statement that she was ‘astonished and under shock’ over her suspension.

The player is now the highest-ranked singles player to test positive for a banned substance since Russian star Maria Sharapova in 2016.

Yastremska, who reached the fourth round of Wimbledon in 2019, said on Twitter: "I am 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.

“I firmly state that I have never used any performance-enhancing drugs or any prohibited substances.

"Only a very low concentration of mesterolone metabolite was detected in my urine.

"Given that low concentration and 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 has been suspended from January 7 and as it stands she will be unable to compete in next month’s Australian Open. 

A full hearing into the case will take place in due course.