Maria Sharapova, the five-time tennis Grand Slam winner, will face an anti-doping panel in London on Wednesday after taking the banned drug meldonium.
The 29-year-old Russian failed a doping test at the Australian Open in January.
Meldonium, a heart disease drug, was added to the World Anti-Doping Agency's banned list on 1 January.
The International Tennis Federation panel could issue a four-year-ban, but experts say a six-month or 12-month punishment is more likely.
That is because Wada admitted in April that scientists were unsure how long meldonium stayed in the system.
It even suggested athletes who tested positive for the substance before 1 March could avoid bans, provided they had stopped taking it before 1 January.
However, Sharapova has already admitted she continued taking meldonium past that date, claiming she was unaware it had been added to the banned list as she knew it by another name - mildronate.
The former world number one also revealed she had been taking meldonium for 10 years on the recommendation of her doctor for medical reasons.
"It is very important for you to understand that, for 10 years, this medicine was not on Wada's banned list and I had been legally taking that medicine," she said.
What is meldonium?
The Latvian-made drug, widely used by sportsmen and women in eastern Europe, is said to benefit athletes by increasing stamina and endurance.
Sharapova's case is the most high-profile but there have been almost 300 positive samples so far this year, according to Wada.
They include Belarusian tennis player Sergey Betov, who also tested positive at the Australian Open.
The doubles specialist was cleared last month by the International Tennis Federation on the grounds that he had stopped taking it before 2016.
Sharapova is expected to argue that the health reasons she cited for taking the drug should qualify her for a backdated therapeutic use exemption.
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