Yastremska, 20, was provisionally suspended earlier this month after testing positive to a banned substance in an out-of-competition sample.

The Ukraine world No.29 later raised eyebrows when she was filmed on a Tennis Australia charter flight to Melbourne despite her provisional ban.

Her first application to the International Tennis Federation to remove the provisional suspension was rejected after a ruling by an Independent tribunal.

Yastremska then made an urgent appeal to sport's highest court, which says it has begun arbitration and will deliver a decision by February 3.

"Ms Yastremska seeks to have the challenged decision set aside and her provisional suspension lifted in order to be able to participate in the 2021 Australian Open," CAS said in a statement in the early hours of Wednesday.

"The CAS arbitration has commenced and the parties have agreed to an expedited procedure."

The Australian Open is scheduled to begin on February 8.

Yastremska provided her sample in November and a WADA lab in Montreal found the presence of mesterolone metabolite, an anabolic agent on its prohibited list.

She has denied ever using performance-enhancing drugs, saying she believes the positive test was the result of a "contamination event" and has vowed to clear her name.

"I'm astonished and under shock, particularly given that two weeks prior to this test ... I tested negative at the WTA event in Linz," Yastremska said in a statement earlier this month.

"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."

Yastremska has won three WTA titles and reached the fourth round at Wimbledon in 2019.

She spent two weeks in self-isolation in Dubai after testing positive for COVID-19.

Australian Associated Press