Novak Djokovic has firmed in favouritism to land a record-equalling 22nd grand slam singles crown following the Australian Open scratching of teenage world No.1 Carlos Alcaraz.
Alcaraz and seven-times grand slam women's champion Venus Williams are the latest superstar drawcards to announce that they will miss this month's Open.
Alcaraz, who won his maiden grand slam title at the US Open in September, revealed he suffered a hamstring injury during pre-season training.
"I had worked a lot to reach my best level in Australia. Unfortunately I won't be able to play either the Care A2+ Kooyong (warm-up event) or the Australian Open," Alcaraz posted on social media on Saturday.
"It is a hard moment, but I have to be optimistic, recover and look ahead. See you in 2024 Australian Open."
Alcaraz had only just recovered from a torn abdominal muscle that ruled him out of the season-ending ATP Finals and Davis Cup Finals.
"When I was at my best in pre-season, I picked up an injury through a chance, unnatural movement in training. This time it's the semimembranosus muscle in my right leg," he said.
Alcaraz rocketed to the top of the rankings last year, becoming the youngest man ever to reach No.1 after beating Casper Ruud in the US Open final in New York.
His withdrawal means countryman and reigning champion Rafael Nadal will be promoted to top seed for his title defence when the season's first grand slam gets under way at Melbourne Park on January 16.
But it's Djokovic's stocks that have really soared.
A year after being kicked out of Australia for failing to get vaccinated against COVID-19, the Serbian's fortunes have sky-rocketed.
First Djokovic successfully had his three-year Australian visa ban overturned in November, allowing the nine-time champion to return to Melbourne to hunt down a record-extending 10th Open trophy.
Now his chief challenger is out of the tournament and Djokovic - who this week extended his five-year unbeaten run in Australia to 32 matches in Adelaide - will crucially be bumped up to fourth seed.
The elevation means the 35-year-old is guaranteed to avoid playing a higher-ranked rival - Nadal, Ruud or Stefanos Tsitsipas - until at least the semi-finals.
Alcaraz's absence from the Open follows the retirements last year of women's titleholder Ash Barty, seven-times champion Serena Williams and six-times men's champion Roger Federer.
In another blow, Open organisers announced on Saturday night that Williams' oldest sister Venus was also a late scratching after being injured while practising at the ASB Classic in Auckland.
The 42-year-old was set to play her 22nd Australian Open after being awarded a wildcard.
Twice a finalist at Melbourne Park, Williams is now ranked outside the top 1,000.
Dual Open winner and fellow former world No.1 Naomi Osaka is also in extreme doubt, having not played since September and not featuring at any of the lead-up events in Australia.
The Open draw takes place at Melbourne Park on Thursday.