Erasmus, the World Cup-winning coach in 2019, should take a back seat, former England and British & Irish Lions coach Sir Clive Woodward has said after the first Test, won by the Lions 22-17 at the weekend.
"If South Africa are to stand any chance of levelling the series in Saturday's second Test, Rassie Erasmus must be a suit in the stands playing no part in matchday decisions," Woodward said in his Daily Mail column.
Erasmus had been delivering more messages than water to players in his role.
And Woodward claimed the players were getting mixed messaging from Erasmus instead of Nienaber in the coaches' box.
Woodward said, "It is clear that Erasmus has started taking over again. He is running around in a tracksuit and donning the water carrier bib even though – as [Warren] Gatland observed last week – he never seems to dispense any water, nor even carry a bottle! He never forgets his clipboard, though.
"It looked comical, it was comical, and I am surprised South African Rugby is allowing it to happen.
"Erasmus is still coaching the team in all but name, but that's not his job. He needs to butt out.
"Confusion at the top and a lack of demarcation between the roles of director of rugby Erasmus and South Africa national team coach Jacques Nienaber is killing the Springboks.
"There can only ever be one man in charge in match and on match day – and that has to be the coach," Woodward said.
Erasmus had his day as a coach, he said. He did a brilliant job in building a Springbok team in a short time that was good enough to win a World Cup, but that was his moment.
"Nienaber is now in charge," Woodward said.
He added that while South Africa were world champions, he has never been convinced of their world-beating qualities.
"Their reputation is built pretty much wholly on their dismantling of a complacent and badly distracted England team who were shambolically poor in the 2019 World Cup final. And since then the Boks have hardly played so there has been no opportunity to grow and mature and build on that win," he said.