After 10 long months, slogging through 20 tournaments in 10 different countries, battling against a debilitating injury while winning 47 of 63 hard-fought matches, Alex de Minaur has at last got his just desserts.

He will go, for the first time in his ever-improving career, to the big end-of-season ball, the ATP Finals in Turin.

The Australian number one finally got the good news when Novak Djokovic's announcement that he was withdrawing from next week's showpiece ensured de Minaur and his rivals for the last spot, Andrey Rublev and Casper Ruud, were all guaranteed the last three places in the eight-man tournament at the Inalpi Arena.

It could not have been more timely relief for de Minaur, who immediately then announced his withdrawal from the Belgrade Open, where he was due to play on Wednesday in a final quest to nail down enough points to ensure qualification.

Instead, Djokovic's decision has spared him the trouble of a nail-biting final scrap with Rublev and Ruud, and given him a much-needed four-day break after three straight weeks of gruelling competition in Europe.

It is also an interesting twist of irony as the 25-year-old was forced to withdraw from his Wimbledon quarterfinal against Djokovic with a hip injury that also ruled him out of the Paris Olympics singles.

Djokovic's withdrawal from Turin, citing an injury, means the championship will be without any of Djokovic, Roger Federer and Rafa Nadal for the first time in 23 years.

"I was really looking forward to being there, but due to ongoing injury I won't be playing next week," Djokovic, the Finals' record seven-time winner, wrote on social media, without explaining any more details.

"Apologies to those who were planning to see me."

It will also mean there will be an Australian man gracing the top-eight showdown for the first time in 20 years, since Lleyton Hewitt got to the 2004 final and was beaten by Federer.

The eight-man, week-long tournament begins on Sunday with the two round-robin groups draw being made on Thursday.

There will be, of course, no easy matches for the world number eight with Jannik Sinner, Alexander Zverev, Carlos Alcaraz, Daniil Medvedev and Taylor Fritz making up the rest of the field.

De Minaur has a winning record against Ruud (2-0), Rublev (4-3) and Fritz (5-3), losing ones against Medvedev (3-6) and Alcaraz (0-2), and horribly lopsided ones against Zverev (2-8) and Sinner (0-7).

There will be a prize fund of $US15.25 million ($23.11 million), with the singles champion having the chance to earn a record-breaking $US4.8 million ($7.3 million) — the largest winner's prize on the men's tour — if he can triumph without losing a match.

The news came with the WTA Finals well underway in Saudi Arabia.

Aryna Sabalenka, unbeaten through two matches against Zheng Qinwen and Jasmine Paolini, secured the year-end women's world number one ranking after American Coco Gauff beat defending champion Iga Świątek 6-3, 6-4.

"Despite our head to head, I had a lot of confidence," Gauff said.

"Even when I was playing a little bit sloppy, the games were still going to deuce."

It was just Gauff's second win in 13 matches against Świątek, who returned from two months off at the Finals.

AAP/ABC