The former Under-20 captain was forced out of the action just four minutes into his second Test for the Springboks after damaging his left knee and, after undergoing scans, it was confirmed he has suffered medial collateral and anterior cruciate ligaments.
The injury will require surgery and means the 21-year-old back-row forward is facing a long spell on the sidelines.
South Africa coach Heyneke Meyer said: "Losing Arno is a big blow as he had a very good Test debut last weekend against Italy.
"Luckily he is still very young and I'm sure with the correct medical treatment and rehabilitation we will see him back on the field again in 2014."
- Sports & Recreation