Los Angeles - Serena Williams called on Tennys Sandgren to apologise on Wednesday after the unheralded American exited the Australian Open amid a backlash over his political views.
Sandgren, a devout Christian, bowed out of the quarter-finals in Melbourne in straight sets following scrutiny over his politics and apparent support for far-right groups in the United States.
Williams had been the subject of a Sandgren post on Twitter, with the 26-year-old describing the former world number one's behaviour during a 2015 US Open match against Roberta Vinci as "disgusting."
Williams, who on Tuesday confirmed her comeback at the Fed Cup next month following a near year-long absence due to pregnancy and subsequent birth of her daughter, ripped Sandgren in a post on Twitter on Wednesday.
"@TennysSandgren. I don't need or want one. But there is a entire group of people that deserves an apology," Williams wrote.
"I can't look at my daughter and tell her I sat back and was quiet. No! she will know how to stand up for herself and others - through my example," she added.
Williams had earlier taken aim at Sandgren as the broadcast of his last eight defeat to South Korea's Chung Hyeon got under way.
"Turns channel," the 36-year-old star wrote.
Following his Australian Open defeat, Sandgren lashed out at the "dehumanising" media after wiping his Twitter account.
Among his tweets was one where he appeared to back a debunked online conspiracy in 2016 which linked Hillary Clinton to a supposed child sex abuse ring at a Washington pizzeria.
He also retweeted a video from white nationalist Nicholas Fuentes.
Sandgren had earlier denied that he supported far-right figures and said who he followed on Twitter "doesn't matter".
"I don't. I don't (support them). I find some of the content interesting," he said of the controversial figures.
Turns channel— Serena Williams (@serenawilliams) January 24, 2018
@TennysSandgren I don't need or want one. But there is a entire group of people that deserves an apology. I cant look at my daughter and tell her I sat back and was quiet. No! she will know how to stand up for herself and others- through my example. ??? pic.twitter.com/im2NhoMdN4— Serena Williams (@serenawilliams) January 24, 2018