The ATP and WTA tours’ new joint venture begins Thursday in three Australian cities with plenty of prize money and ranking points at stake.

And the mixed teams United Cup could also help shake off some of the holiday season rust ahead of the Australian Open starting Jan. 16 in Melbourne.

The inaugural United Cup has teams from 18 countries competing in Brisbane, Perth and Sydney through to Jan. 4. Then the three city champions and the next-best performing country from the group stage will meet at Ken Rosewall Arena in Sydney from Jan. 6 to 8 to determine the overall winner.

The tournament offers $15 million in prize money and up to 500 ATP and 500 WTA rankings points.

Nick Kyrgios has pulled out of the Australian team with an apparent ankle injury sustained in an exhibition tournament last week in Dubai. The Wimbledon finalist was expected to lead the Australian team, facing Britain’s Cameron Norrie in Sydney on Thursday night, but withdrew ahead of Wednesday’s scheduled media conference.

Kyrgios was also due to play Rafael Nadal in the most eagerly-anticipated match of the event when Australia meets Spain next week.

“Team Australia update: Nick Kyrgios has withdrawn from the United Cup due to injury,” United Cup organizers tweeted.

Kyrgios’ Australian teammates only learned 10 minutes before the media conference that he would no longer be joining them.

Team captain Samantha Stosur said she hadn’t spoken to Kyrgios about his decision and wouldn’t comment on whether he would be fit for the Australian Open.

“I’m not going to speak for Nick’s summer, we’ve got to leave that for him,” Stosur said.

With Kyrgios out, world No. 24 Alex de Minaur will move into the No. 1 men’s position for Australia and play against Norrie and Nadal, with No. 107 Jason Kubler — the fifth-ranked Aussie male — promoted to the No.2 spot.

Top-seeded Greece is led by world No. 3 Stefanos Tsitsipas and No. 6-ranked woman Maria Sakkari. World No. 1 Iga Swiatek and No. 11 Hubert Hurkacz will lead second-seeded Poland, with third-seeded United States featuring world No. 3 Jessica Pegula, ninth-ranked Taylor Fritz, world No. 11 Madison Keys and No. 19 Frances Tiafoe.

Nadal will team with world No. 13 Paula Badosa for Spain, while Italy will have world No.16 Matteo Berrettini and Martina Trevisan.

Each host city will feature two groups of three countries, competing in a round-robin format. Each tie will have two men and two women’s singles matches and one mixed doubles match to be played over two days.

Among other matches on Thursday’s opening day, the United States plays Czech Republic in a day Group C encounter, also in Sydney. In Brisbane, it’s Italy vs. Brazil in a day Group E match and Switzerland vs. Kazakhstan at night in Group B.

At Perth, Greece plays Bulgaria in Group A and France plays Argentina later in a night Group F match.