Serena Williams has accused anti-doping authorities of discrimination over how often she has been singled out for random drugs testing.

The Wimbledon runner-up has been tested more than any other tennis player so far in 2018 and spoke out on Twitter on Tuesday night after another visit from doping officials.

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“...and it’s that time of the day to get ‘randomly’ drug tested and only test Serena,” she posted. “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 later added, in another tweet, that she was “ready to do whatever it takes to have a clean sport”.

Williams has previously raised questions over how often she is singled out after a Deadspin report in June revealed that she had been tested five times in 2018 when other players had not been tested at all. At Wimbledon, she called her treatment by the US Anti-Doping Agency (Usada) “shocking”.

“It’s only June, I’ve been tested five times,” she said. “I despise having people in our sport that aren’t being honest. I’m totally OK with testing and I encourage it. What I want to know is everyone is getting tested?

“It’s all about equality. If that’s testing everyone five times, let’s do it. It’s just about being equal and not centring one person out. Just due to the numbers, it looks like I’m being pushed out.”

Play Video 1:50 Serena Williams and Roger Federer voice frustrations with tennis doping tests – video

Usada says the latest test was not conducted by them and in June said: “We test only in accordance with international standards and would never conduct testing in an unfair way.”

Williams gave birth to her daughter Olympia in September 2017 and returned to the sport five months later in February this year. She last won a major title when she beat her sister Venus in the 2017 Australian Open final while two months pregnant. Her remarkable run at Wimbledon came to an end this year when she was beaten by Angelique Kerber in the final, though her runner-up place ensured a return to the top 30 of the women’s rankings.