Serena Williams says she would have been banned for 20 years and had some of her Grand Slam titles taken away if she had committed the same anti-doping offence as men's world number one Jannik Sinner.
Italy's Sinner, 23, is serving a three-month doping ban after reaching a settlement with the World Anti-Doping Agency (Wada) over two positive drugs tests last year.
Former world number one Williams, winner of 23 Grand Slam titles, claimed in 2018 that she was a victim of "discrimination" over the volume of drug tests she was required to carry out.