July 25 (UPI) -- Serena Williams cited "discrimination" when she wrote about once again being selected for a random drug test.
Williams voiced her disapproval of the selection for another drug test Tuesday on Twitter.
"... and it's that time of the day to get 'randomly' drug tested and only test Serena. Out of all the players it's been proven I'm the one getting tested the most. Discrimination? I think so. At least I'll be keeping the sport clean."
"But I'm ready to do whatever it takes to have a clean sport so bring it on. I'm excited."
Williams also commented on the drug tests in May, saying she was tested twice in the same week. At the time, she was ranked No. 454 in the world. She now sits at No. 27 in the Women's Tennis Association world rankings.
The 23-time Grand Slam champion withdrew from the Australian Open and the fourth round of the French Open before making it to the 2018 Wimbledon final. She fell in straight sets to Angelique Kerber at the All England Club.
...and it’s that time of the day to get “randomly” drug tested and only test Serena. Out of all the players it’s been proven I’m the one getting tested the most. Discrimination? I think so. At least I’ll be keeping the sport clean #StayPositive— Serena Williams (@serenawilliams) July 25, 2018
The United States Anti-Doping Agency said Williams had been tested five times this year before she wrote her message about a sixth test. No. 1 Simona Halep has not been tested in 2018. Fellow Americans Sloane Stephens and Madison Keys have each been tested once.
Venus Williams and CoCo Vandeweghe have each been tested twice this year. The top 20 players have been tested a combined six times, the same amount of times as Williams.