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 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 1 March could avoid bans, provided they had stopped taking it before 1 January.