Keshav Maharaj has suffered a complete rupture of his left achilles tendon.
The Proteas spinner won a successful appeal for lbw against Kyle Mayers in the last over before lunch of the second Test against the West Indies at the Wanderers on Saturday.
In celebrating, Maharaj collapsed and was stretchered off the field.
The 33-year-old is due to see a surgeon on Monday.
REPORT: Proteas crush Windies at Wanderers
Maharaj has been South Africa’s leading Test spin bowler since making his debut in 2016 but has more recently become a regular in the ODI team.
The Proteas have no Tests scheduled until December but his injury will mean that he misses the ODI series against the West Indies which starts in East London on Thursday – and could put him in doubt for the World Cup in India in October.