Nick Kyrgios is in line for a pre-Australian Open blockbuster with defending champion Rafael Nadal after Australia was drawn in the same pool as Spain for the inaugural United Cup.
Alex de Minaur and Jason Kubler were the other men's singles players named in Australia's eight-strong line-up for the $US15 million ($A23m) mixed teams' event from December 29 to January 8.
But it will be Kyrgios getting a crack at Nadal after the Wimbledon finalist secured Australia's year-end top ranking when de Minaur was unable to reach the quarter-finals of last week's Paris Masters.
Under United Cup rules, the two nations' No.1s will clash, with the respective No.2s to feature plus two women's singles match-ups determined on the same basis.
A mixed doubles encounter could potentially decide the five-match ties.
Kyrgios could also pair up with old flame Ajla Tomljanovic after the three-times grand slam finalist was named as the No.1 female in the Australian team alongside Zoe Hives, Maddison Inglis and doubles stars John Peers and Samantha Stosur.
But it will be Kyrgios's showdown with Nadal that will likely sell out Ken Rosewall Arena after Group C and Group D - which comprises the USA, Germany and Great Britain - were drawn to play the round-robin stages in Sydney.
Kyrgios and Nadal were slated to meet in this year's Wimbledon semi-finals before the great Spaniard was forced to pull out with an abdominal tear.
Kyrgios predicted their showstopper would be "the most-watched match of all time".
United Cup officials also revealed women's world No.1 Iga Swiatek would be another headline performer at the maiden running of the new summer-opening event.
Team Greece, led by world No.3 Stefanos Tsitsipas and the sixth-ranked Maria Sakkari, were named top seeds.
Swiatek and world No.11 Hubert Hurkacz will spearhead second-seeded Poland, with third seeds the USA featuring a wealth of talent including world No.3 Jessica Pegula, ninth-ranked Taylor Fritz, world No.11 Madison Keys and charismatic US Open semi-finalist Frances Tiafoe.
Nadal will team up with world No.13 Paula Badosa for Spain, while emerging tennis powerhouse Italy can call on 2021 Wimbledon runner-up Matteo Berrettini and rising star Martina Trevisan.
France round out the top six seeds, led by Arthur Rinderknech and WTA Finals winner and world No.4 Caroline Garcia.
Other notable entries include Norway's world No.4 Casper Ruud, Germany's Alexander Zverev, and Switzerland's Belinda Bencic and Stan Wawrinka, along with dual Wimbledon champion Petra Kvitova of the Czech Republic.
The top six WTA ranking-qualified countries, top five ATP ranking-qualified countries and the top five combined entry countries have been admitted to the competition.
The final two nations (one ATP and one combined entry) will be admitted to the competition on November 21.
Brisbane, Perth and Sydney will each host two groups of three countries competing in a round-robin format from December 29 to January 4.
The winners of each group will play off, with the city winners advancing to the United Cup's final four in Sydney from January 6-8.
The next best performing team from the group stages will complete the quartet.
UNITED CUP DRAW:
PERTH
A: Greece, Belgium, ATP 6
F: France, Croatia, Argentina
SYDNEY
C: USA, Germany, Czech Republic
D: Spain, Australia, Great Britain
BRISBANE
B: Poland, Switzerland, Combined 6
E: Italy, Brazil, Norway
