Kyrgios was a major drawcard for the new mixed-gender tennis event, which will be played across Sydney, Brisbane, and Perth from Thursday.
He cited the need to recover from multiple injury niggles ahead of the Australian Open next month.
ULTIMATE GUIDE: Everything you need to know about the United Cup
His team told the Sydney Morning Herald the star suffered an ankle injury in Dubai, and must use the next fortnight to recover ahead of the Open.
Kyrgios, 27, had days earlier spruiked the United Cup and said how excited he was to be competing in what would be his first Australian appearance since winning the Australian Open doubles final with Thanasi Kokkinakis in January.
“There’s nothing better, to play the Australian summer is one of my favourite times of the year,” Kyrgios said.
“Obviously being home, but being able to play in Sydney, in front of the home fans, my family, my friends, there’s nothing more that I love.”
Kyrgios drew criticism – including from Lleyton Hewitt and Alex de Minaur – last month for refusing to represent Australia at the Davis Cup.
Watch Team Australia take on the world in the United Cup, live and exclusive on 9Now and Stan Sport.
In his true combative style Kyrgios poked fun in an Instagram post as he flew to the Middle East to compete in rich, short tournaments.
”Maybe if Australia embraced me a little bit more, I would play it and bring home the trophy,” he said earlier this month.
“It’s not always easy for me to erase everything in Australia that’s said negatively about me or my family.
“You don’t need that – so it’s interesting that they really want me to play, but are always criticising.”
Kyrgios also took to Instagram to suggest Ash Barty did not deserve the Newcombe Medal.
It will be intriguing to see the reception he gets at Melbourne Park when he steps out for the January grand slam.
For a daily dose of the best of the breaking news and exclusive content from Wide World of Sports, subscribe to our newsletter by clicking here!