Wicketkeeper-batsman Quinton de Kock is in a race against time to be fit for the World Cup, Cricket South Africa said on Saturday.
De Kock tore ankle ligaments on the third morning of the first test against the West Indies in Pretoria.
The usual recovery period for such an injury is six to 12 weeks, putting in doubt his participation in the global event in Australia and New Zealand starting on Feb. 14.
The Proteas had hoped to have him fit for the second test against West Indies starting on Boxing Day, but the severity of his injury, sustained in the warm-up before the day's play, became clear following MRI scans.
The team have a readymade replacement in AB de Villiers to keep wicket, but De Kock has formed a successful opening partnership with Hashim Amla in one-day cricket and it is there his loss would be most keenly felt.
The 22-year-old, who has made six centuries and four fifties in 35 innings at an average of 43.58, has the ability to score quick runs with his swashbuckling style.
With De Villiers to take the gloves for the second test in Port Elizabeth, the Proteas selectors must now decide whether to hand a debut to the reserve batsman in the squad, Temba Bavuma, or play an extra bowler, likely to be spinner Robin Peterson.
South Africa won the first test by an innings and 220 runs on Saturday.
