Head was on nine, facing his eighth delivery, when he was struck on the left glove attempting a pull off Coetzee. He received treatment onfield from the Australian medical staff before continuing to bat but only faced three more deliveries before retiring hurt in clear discomfort. He was sent to hospital for an x-ray and Australia coach Andrew McDonald confirmed after the match that the x-ray had shown a fracture.

He will have further scans on Saturday with more information on the severity of his injury and a timeline for his recovery to be determined. Head did return to the ground at the end of the match but had his left hand in a splint.

"At this stage, it's a confirmed fracture and how long that timeframe is, we're yet to determine that so fingers crossed clearly with the World Cup fast approaching," McDonald said post-match.

"I'm not a medical person, but I think it's a little bit higher up than the actual [index] finger itself. But I don't know the actual terminology. It's in a joint somewhere so I won't go into the medical specifics. But, yeah, a confirmed fracture and to be assessed again tomorrow with another scan."

Australia's chase of 417 suffered early dents when they were reduced to 22 for 2, but Head made a strong start. After he was struck, he received treatment on the field and opted to continue, and seemed more than able to when he whipped Marco Jansen over deep backward square for six. He toe-ended the next ball just short of Kagiso Rabada at mid-off, taking the injured hand off the bat while playing the stroke. He immediately removed his glove at the non-striker's to asses his hand again.

The next ball he faced at the start of the next over he made room to cut but Coetzee followed him and cramped him as he tried to flay it through the offside. He immediately winced in severe pain after playing the stroke and walked straight to the dressing room, informing stand-in South Africa captain Aiden Markram and the umpires that he could not continue as he walked off. Australia were 53 for 2 in the ninth over at the time and ended up being bowled out for 252 with Head not returning to bat when the ninth wicket fell.

The injury will doubtless increase speculation that Marnus Labuschagne, who was not part of Australia's initial World Cup squad, could force his way into the final playing group. Labuschagne came on as a concussion substitute in the first ODI and scored an unbeaten 80 in a match-winning cause, and followed that up with 124 in the second game.

Head's injury adds to Australia's long list of concerns heading to the World Cup. Pat Cummins (wrist fracture), Steven Smith (wrist tendon), Mitchell Starc (groin), Glenn Maxwell (leg) are all coming off lay-offs and hoping to be fit for the three-match ODI series against India that starts on September 22 in the lead-up to the World Cup.

Ashton Agar also only played one game in South Africa coming off a calf strain before heading home to Perth for the birth of his first child. He was supposed to play at least two but he was unavailable for games two and three of the series due to soreness before flying home and he is unlikely to return to the squad until after the India ODI series.

Cameron Green is coming off a concussion in game one of the South Africa series but McDonald was hopeful he would be available for the fifth and final match of the series on Sunday after serving his mandatory eight-day rest period.

"He's been cleared by the medical team," McDonald said. "So he's just working away getting prepared. Hopefully, he's available for game five. That's the plan at this stage. We'll be able to have some training tomorrow, assess that and there will be some forced changes and we'll have some guys potentially a little bit sore. We'll have to manage those guys as well."

Spencer Johnson is still unavailable due to a hamstring injury and Mitch Marsh won't bowl in Sunday's final ODI with McDonald confirming he would return to bowling in India after some ankle soreness flared up during the Ashes series following an unexpected heavy workload.

But with Head set to miss Sunday's game and potentially the start of the World Cup, Marsh looks set to move up to open given the form he showed in India earlier in the year.