Springbok captain Siya Kolisi was forced off after just 22 minutes of his comeback game in Racing 92's Champions Cup round of 16 match in Toulouse on Sunday.
The 32-year-old two-time World Cup winner, who was replaced at flanker by Ibrahim Diallo, appeared to have injured his right ankle.
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Kolisi, who joined Racing after last year's World Cup triumph, was making his return to competitive rugby after more than a month out following surgery on a finger in his right hand.
Toulouse welcomed back flyhalf Romain Ntamack after an eight-month lay-off which ruled him out of France's bid to win the World Cup on home soil.
Toulouse won the match 31-7.
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