The Springboks play Ireland in Dublin tomorrow night.
“Robbie has been struggling with a pinched nerve in his neck for a few months,” said Springbok team doctor Craig Roberts.
“It flared up again after our training session on Tuesday afternoon and he was withdrawn from all training for the rest of the week.
“We also consulted with the Golden Lions’ medical team and reviewed his scans. After seeking specialist opinions it was decided that, due to his current functional impairment, it was in his best interests for the long term to withdraw him from the tour.”
Ntubeni, who is currently in London with Western Province, will join the Springbok squad in the English capital after their match on Sunday afternoon against Saracens. Coetzee will return to South Africa in the coming days.