Serena whacks divisive tennis star in public burn

Serena Williams has unleashed a veiled attack on unheralded American tennis hope and politically divisive compatriot, Tennys Sandgren.

Williams gave a very public 'thumbs down' to her fellow American on Wednesday before Sandgren's quarter-final at the Australian Open.

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"Turns channel," the 23-time major winner tweeted as Sandgren took the court in his match against fellow outsider Hyeon Chung.

The missive is being widely read as a reference to Sandgren's support for the politics of US President Donald Trump.

Williams isn't defending her title at Melbourne Park after the birth of her first child in September.

As a Jehovah's Witness, the 36-year-old does not vote but has previously expressed support for former president Barack Obama.

She is a UNICEF goodwill ambassador and has supported fundraising efforts for marginalised communities and anti-violence initiatives.

Sandgren's run to the last eight at the Open has brought to light his support for Trump and interest in nationalist and alt-right politics.

The 26-year-old Tennessee native deleted all but one of his tweets in response to scrutiny of his political views.

Bizarre scenes preceded Sandgren's 6-4 7-6 6-3 loss against Chung as a fire alarm went off at Rod Laver Arena just before play got underway.

A computer malfunction was blamed as the cause for the strange pre-cursor to the match.