Serena Williams has questioned the randomness of anti-doping measures in tennis and claimed she is tested more than other players due to "discrimination".

The 23-time grand slam champion complained about a lack of consistency in the tests ahead of Wimbledon, where she reached the final despite giving birth to her first child last September.

And, following a visit from anti-doping officers on Tuesday, the 36-year-old has now suggested there are discriminatory reasons for her having been tested more regularly than her rivals, as shown by the United States Anti-Doping Agency's (USADA) online database.

"And it's that time of the day to get 'randomly' drug tested and only test Serena," Williams posted on Twitter.

"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."

She added: "But I'm ready to do whatever it takes to have a clean sport so bring it on. I'm excited."

As of July 20, Williams had been tested five times in 2018 - more than double the amount of any other female player in the database.