World No. 1 Novak Djokovic will begin his 2024 campaign in the mixed teams United Cup in Australia, while Rafael Nadal was left off the Spain team, which was confirmed on Friday.

Nadal has been troubled by injuries.

Serbia will be led by Djokovic at the competition, which runs from December 29 to January 7 in Sydney and Perth as he prepares to defend his Australian Open crown. Prior to suffering a hip injury at the first Grand Slam of the year in 2023, Nadal was a member of the Spain team. Since having surgery in June, he has been unable to play.

Tennis Australia chief Craig Tiley said this month Nadal planned to make his return to Grand Slam tennis at the Australian Open, which follows the United Cup.

Nadal responded on social media by thanking Tiley for his "confidence", without confirming if he would appear.

There are ATP events in Brisbane, Adelaide and Auckland in early January that Nadal could also use to prepare for the Australian Open.

The United Cup will include five of the top 10 women and nine of the top 20 men in the globe, with the defending champion United States being one of the favorites, led by Jessica Pegula and Taylor Fritz.