Travis Head is in a race against time to be fit for the World Cup after he suffered a fractured hand in Australia's horror 164-run loss to South Africa in the fourth one-day international at Centurion.
Head was struck a painful blow on his left hand from a rising ball by Proteas paceman Gerald Coetzee before retiring hurt two overs later on 17, as Australia were knocked over for 252 on Friday (Saturday AEST) in response to South Africa's mammoth 5-416.
The unavailability of Head, an explosive weapon at the top of the order, would place a dent in Australia's hopes to win the World Cup, now just three weeks away.
"It's a confirmed fracture," Australia coach Andrew McDonald said.
"As to the nature of what sort of time frame that lends itself to, that will be assessed tomorrow.
"I think he's going to go in for more scans tomorrow to get a detail of that, then we'll work out the management of it from there.
"I'm not a medical person but I think it's a bit higher up than the finger itself ... it's in a joint (in the hand) somewhere.
"Fingers crossed with the World Cup fast approaching."
If Head was to miss the start of the World Cup, Mitch Marsh could move to the top of the order alongside David Warner.
That would potentially open the door for Australia's selectors to squeeze the in-form Marnus Labuschagne into their 15-man squad, as a middle-order batsman.
Alex Carey's brilliant solo 99 was the only shining light for the tourists, who were powerless to prevent South Africa from emphatically levelling the series 2-2.
Australia's bleak chase ended when Carey became the third Aussie, after Labuschagne (20) and Marcus Stoinis (18), to glove a short ball to wicketkeeper Quinton de Kock.
It capped the tourists' second defeat by 100-plus runs in three days and their second heaviest loss in all ODIs against South Africa.
Earlier, Heinrich Klaasen, with an extraordinary 174 off 83 balls, and David Miller (82no off 45) belted 19 fours and 18 sixes between them and shared in a blistering 222-run fifth-wicket stand from just 94 deliveries.
Klaasen's was the fourth fastest ODI ton by a South African, bettered only by AB de Villiers (twice) and Mark Boucher.
When he finally holed out to Nathan Ellis in the deep off the final ball of the innings, he fell four runs shy of de Kock's venue record of 178.
After smashing 173 from the last 10 overs, the Proteas amassed their fifth-highest total in ODIs and their best at this venue, while it was the third biggest score ever yielded by Australia in the 50-over format.
None of the tourists' bowlers were spared in the onslaught, with only Michael Neser (1-59) in his first ODI since 2018 going at under a run-a-ball.
Legspinner Adam Zampa was plundered for 0-113 from 10 overs, equalling countryman Mick Lewis's unwanted record (against the Proteas in 2006) for the most runs conceded by a bowler in an ODI.
"Sometimes you look at what you can do better but also you've got to pay credit to the ability of the opponent," McDonald said.
"They put extreme pressure on us and that was some serious hitting.
"I don't think we've seen too many innings like that before."
The winner-takes-all fifth game is at Johannesburg this Sunday.