The Court of Arbitration for Sport (CAS) started hearing Simona Halep's appeal against a doping suspension that could end her tennis career.
The former Wimbledon and French Open champion arrived on Wednesday at the top court in global sport in Lausanne for three-day proceedings, hoping that her provisional suspension will be lifted.
The 32-year-old Romanian has been provisionally suspended since October 2022 after testing positive for roxadustat, a banned drug that leads to production of red blood cells, at the U.S. Open that year.
Halep was also charged with another doping offence last year due to irregularities in her athlete biological passport (ABP), a method designed to monitor different blood parameters over time to reveal potential doping.
Halep has consistently denied all the charges.
The former world number one has blamed contaminated licensed supplements for her positive test at the U.S. Open. She has accused the International Tennis Integrity Agency (ITIA) of charging her with an ABP violation after the group of experts who assessed her profile learned her identity.
An independent tribunal accepted Halep's argument that she had taken a contaminated supplement but determined the volume she ingested could not have resulted in the concentration of roxadustat found in her positive sample.
Halep will not make any statement until the proceedings ends, CAS said. The court said it was unclear when a ruling might be made.
Halep told Euronews in December that if the court dismisses her appeal, she could be compelled to retire.
"It's catastrophic if it's going to be four years," she said. "I don't know how I will handle it. Probably it will be the end of my career."
— Additional input from Reuters