Greek tennis star Stefanos Tsitsipas on Wednesday told rival Nick Kyrgios to "enjoy his holidays", after the Australian stunned his team by withdrawing from the United Cup at the last minute.

Kyrgios pulled out of the mixed teams event on the eve of the inaugural tournament, to be held in Sydney, Brisbane and Perth.

"It is not a surprise, I hope he enjoys his holidays," Tsitsipas, the main talent on the eight-player Greek side in Perth, said.

The pair have had a fractious relationship which came to a head at Wimbledon this year when Tsitsipas said his Australian opponent had an "evil side", after a bad-tempered third-round match.

That contest descended into mayhem when a frustrated Tsitsipas hit the ball into the crowd after losing the second set and Kyrgios told the umpire his opponent should be kicked out of the tournament.

The bad feeling bubbled up again in post-match press conferences, with Tsitsipas calling him "a bully".

"I don't know where all of his energy comes from," Tsitsipas said Wednesday of Kyrgios. "There is so much of it, I don't know how he does it.

"You cannot concentrate on your own game, there is so much noise coming from the other side of the net. It's distracting, you have to be at your best to overcome it all."

Eighteen countries will compete in the United Cup across 11 days from Thursday, with the three cities all hosting group games in a round-robin format before a finals series in Sydney.

Ties comprise two men's and two women's singles matches and one mixed doubles.

Tsitsipas said the Greek team was psyched up about trying to lead a minor tennis nation to big achievements in the new tournament.

"We are all doing this together," he said of the squad's spirit.

"Our team all have their eyes on the prize, but this (winning) can only be achieved by combining forces and committing every day.

"When it comes to tennis, team events are my favourite. I have a lot of faith in the players on our squad, we are all striving for excellence together.

© Agence France-Presse