Former world number one, Serena Williams says she is a victim of “discrimination” after revealing that she is the most drug tested American tennis player.

The twenty-three-time Grand Slam champion made the claim in a tweet on Tuesday, after doping officials visited her.

The thirty-six-year-old had previously expressed frustration about the volume of her tests earlier this month.

In addition, website Deadspin also revealed last month that Serena was tested out of competition by the US Anti-Doping Agency on five occasions this year.