In a major blow for Australia's immediate and long-term prospects, Smith hurt his right little finger during a crucial moment of the World Test Championship final at Lord's on Friday.
Wearing a helmet while standing closer in slips than normal, the former Australia captain put down a regulation chance off Mitchell Starc that would have dismissed Proteas captain Temba Bavuma for only two.
Smith immediately left the field in immense pain after spilling the catch that would have put Australia in the box seat to claim back-to-back WTC titles.
Instead, Bavuma combined with Aiden Markram for an unbeaten 143-run stand to put South Africa in reach of a famous victory on 2-213, just 69 runs from the winning line.
The 36-year-old was assessed by medical staff in the Lord's change rooms, before being taken to hospital for X-rays and further treatment.
As of an hour after stumps, Smith was still in hospital and the Australian team had no further update on his condition.
"We weren't really up to speed in terms of how gruesome the injury was," Australia assistant coach Daniel Vettori said.
"We just heard there was a fear of the compound fracture or dislocation, something of that nature.
'We'll just wait and see what comes back after he gets back from hospital."
A compound dislocation is when bone pierces the skin, which could mean Smith needs surgery and a long rehabilitation.
One of the greatest red-ball batters of all-time, Smith's looming absence will be a major blow after scoring four centuries from his last six Tests in a stunning late-career resurgence.
But Smith's misfortune could give out-of-form teammate Marnus Labuschagne a reprieve.
The 30-year-old Labuschagne averaged less than 30 during this WTC cycle during the past two years, with his last century coming back in July 2023.
A long-term No.3, Labuschagne moved up to open for the first time in his Test career for this match.
But the promotion failed to snap him out of his lean spell, making 17 and 22.
Teenage tyro Sam Konstas, who announced himself last Boxing Day, is almost certain to be given an opportunity as opener for Australia's first tour of the Caribbean in 10 years.
If Smith can't play, Konstas could slot back in to open with Usman Khawaja, while Labuschagne would likely drop down to No.3.
But even Khawaja, who turns 39 later this year, is under pressure to keep his Test career going after scores of 0 and 7 in this Test.
Australia's first Test begins in Barbados in 12 days on June 25, followed by matches in Grenada and Jamaica.
This AAP article was made possible by support from Amazon Prime Video, which is broadcasting the World Test Championship final.
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