The five time grand slam winner Maria Sharapova, will appear before an anti-doping panel in London tomorrow after taking the banned drug meldonium.
The 29-year-old Russian failed a doping test at the Australian Tennis Open in January.
Meldonium, a heart disease drug, was added to the World Anti-Doping Agency's banned list on January 1st.
The International Tennis Federation panel could issue a four-year-ban but experts say a six to 12 month punishment is more likely.
That is because Wada admitted in April that there was a lack of scientific evidence about how long meldonium stayed in the system and it suggested athletes who tested positive for the substance before March 1st could avoid bans, provided they had stopped taking it before January 1st.
However, Sharapova said she had continued taking it past that date as 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 admitted she had failed to properly read advice sent out by anti-doping authorities ahead of the ban.
After admitting she had failed the drug test, Sharapova revealed she had been taking the 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 for the past 10 years," she said.
The Latvian-made drug is said to benefit athletes by increasing stamina and endurance. It was widely used by sportsmen and women in eastern Europe, in particular, ahead of its prohibition.
A recent study suggested almost 500 athletes may have been taking meldonium at the 2015 European Games
Sharapova has been the highest-earning female athlete in the world in each of the past 11 years, according to the Forbes list.
Her case has been the most high-profile relating to meldonium since the ban was brought in - there have been almost 300 positive samples so far this year, according to Wada.
Sharapova is expected to argue that the health reasons she cited for taking the drug should qualify her for a backdated therapeutic use exemption.