Tennys Sandgren must be wishing he had never made his brief foray into the spotlight at the Australian Open.The unseeded 26-year-old reached the quarter-finals with a surprise victory over Dominic Thiem, before crashing out to Chung Hyeon in straight sets.It is the South Korean who will face Roger Federer in the last four, but much of the attention was detracted from Chung's progress due to a dispute surrounding his opponent's political beliefs.Millions of fans will no doubt have been delighted by the US player's progress - that is, until his Twitter account started to attract attention.Sandgren has repeatedly batted away questions over his social media activity, amid suggestions he sympathises with the alt-right.It's fair to say that even now he is out of the Open, the row continues to upset many in the tennis world. Not least, Serena Williams.The seven-time winner has understandably been infuriated by a string of tweets, which have now been deleted, sent from the account, including two about her.The first claimed that "any day Serena loses is a good day", as quoted by News.com.au.Sandgren also called her "disgusting", believed to be a comment on her on-court behaviour during a 2015 match against Roberta Vinci.As he took to the Rod Laver arena to face Chung, she responded with a simple tweet: "Turns channel."

Williams, of course, is not taking part Down Under as she continues to recover from giving birth, instead targeting a return at the Fed Cup.

Williams takes aim again 

The action in Australia has evidently grabbed her attention, though, as she later posted another tweet aimed at her new-found enemy.

Insisting "there is an entire group of people that deserves an apology", it will certainly be interesting to see whether Sandgren replies directly.

In the meantime, he used his press conference to read out a pre-prepared statement from his phone before taking questions from reporters.

"You would rather perpetuate propaganda machines instead of researching information from a host of angles and perspectives while being willing to learn, change, and grow," he said, per CNN.

"You dehumanize with pen and paper and turn neighbor against neighbor. In so doing, you may actually find you're hastening the hell you wish to avoid, the hell we all wish to avoid."

That is unlikely to cut any ice with his critics, Williams the most vocal of them all.