Serbia will face the Czech Republic and China, while top seeds Poland meet Spain and a yet-to-be-determined nation at the event from December 29 to January 7 - a key lead-up to the Australian Open.

Defending champions the United States, spearheaded by Taylor Fritz and Jessica Pegula, will also play in Perth, drawn alongside Australia and Britain.

Second seeds Greece, boasting Stefanos Tsitsipas and Maria Sakkari, will begin in Sydney against a Canada team featuring Felix Auger-Aliassime and Leylah Fernandez.

Grand Slam champion Angelique Kerber will also be in Sydney to make her return from maternity leave, representing Germany alongside Alexander Zverev against France and Italy.

Borna Coric and Donna Vekic lead Croatia against the Netherlands and Casper Ruud's Norway.

Each team - with three men and three women - will go through a round-robin format, with ties comprising one men's and women's singles and a mixed doubles clash.

Group winners in each city advance to the quarter-finals, along with the best runner-up.

The semi-finals and final will be played in Sydney with US$15 million in prize money and ATP and WTA rankings points at stake.

Draw for the United Cup:

Perth

Group A - Poland, Spain, TBC

Group C - United States, Britain, Australia

Group E - Czech Republic, China, Serbia

Sydney

Group B - Greece, Canada, TBC

Group D - France, Italy, Germany

Group F - Croatia, Netherlands, Norway