Simona Halep has vowed to "fight until the end" to prove she never knowingly took a banned substance after the former world No 1 was handed a provisional suspension for failing a doping test.
The International Tennis Integrity Agency (ITIA) confirmed Halep tested positive for roxadustat during the US Open in August, a substance which stimulates the production of red blood cells and is used to treat anaemia and kidney problems.
The two-time Grand Slam champion subsequently released a statement on social media expressing her shock and said she is determined to clear her name.
"Today begins the hardest match of my life: a fight for the truth," the 31-year-old Romanian wrote on Twitter. "I have been notified that I have tested positive for a substance called roxadustat in an extremely low quantity, which came as the biggest shock of my life.
"Throughout my whole career, the idea of cheating never even crossed my mind once, as it is totally against all the values I have been educated with. Facing such an unfair situation, I feel completely confused and betrayed.
"I will fight until the end to prove that I never knowingly took any prohibited substance and I have faith that sooner or later, the truth will come out.
"It's not about the titles or the money. It's about honor, and the love story I have developed with the game of tennis over the last 25 years."
Halep, the 2018 French Open and 2019 Wimbledon champion is the highest-profile player to fail a drugs test since Maria Sharapova in 2016.
Halep had ended her season in mid-September after having nose surgery, and has struggled with various injuries over the past two years.
Speaking in September, she said that earlier in the year she had suffered mental problems and had considered ending her career but she began working with Serena Williams' former coach Patrick Mouratoglou and her form briefly rebounded.
She reached the semi-finals at Wimbledon this year and won in Toronto to reach No 6 in the rankings in August before slipping back to ninth.
The ITIA, which oversees tennis' anti-doping programme, said it had informed her on October 7 that she was being provisionally suspended.
It said Halep had exercised her right to have her 'B' sample analysed, which confirmed the presence of roxadustat.
In a statement, it said: "While provisionally suspended, the player is ineligible to compete in or attend any sanctioned tennis events organised by the governing bodies of the sport."