The American had previously expressed frustration about the volume of her tests earlier this month.
“Out of all the players it’s been proven I’m the one getting tested the most. Discrimination? I think so,” said the 36-year-old.
Serena is a 23-time Grand Slam singles champion.
It was eventually marked as a “missed test” – three of those would result in a Usada doping violation.
At the time of publication of the Deadspin article, Williams had been tested more than twice as many times as other top American players – male or female – including US Open champion Sloane Stephens (one) and sister and multiple Grand Slam winner Venus Williams (two).
Williams was asked about the findings of the report during Wimbledon earlier this summer.