Ahead of Saturday's opening November international against Ireland, South Africa have withdrawn Ruan Pienaar from their northern hemisphere tour squad and called up scrumhalf Jano Vermaak as a replacement.

Pienaar failed a fitness test for Saturday’s test at the Aviva stadium and was also a major doubt for the following weekend’s clash with England.

The 30-year-old picked up a knee ligament injury in the Springboks’ four-point loss to New Zealand in Wellington in September and has been out of action since.

"Ruan was re-assessed on Tuesday morning following the on-field fitness tests from Monday, and unfortunately he has developed some swelling and puffiness around the knee, indicating that he is not yet ready to partake in full training and playing in a match," Springbok team doctor Craig Roberts said in an SARU statement on Tuesday.

“He needs a few more weeks of rehabilitation before he’ll be ready to return to play and hence we’ve taken the decision to rule him out of the tour.”

Springbok coach Heyneke Meyer said he was disappointed to lose Pienaar.

“We’ll miss his experience, especially when it comes to playing rugby in the northern hemisphere, but luckily Jano knows our structures and should not have a problem to slot back in,” said Meyer.

Vermaak, who played in three tests in 2013 and has been part of the squad for most of the previous two seasons, will join the Boks in Dublin by Wednesday.

South Africa also play tests against Italy and Wales on their tour.