Nienaber told South African media ahead of Saturday's opening pool game between the All Blacks and Springboks that he would not be surprised if the New Zealanders unleashed something new in the game.
"New Zealand have always got an innovative play in the bank. As a defence coach, I always look forward to what they're going to do next," he said.
Nienaber believed the threat came from the greater mobility and skill work developed among the All Blacks' pack.
"In the past, and here I'm talking as far back as 2010, the attack didn't have the discipline to keep the ball for 40 phases or more. The forwards didn't have the skill set.
"Now that front row forwards can pass, sidestep, chip kick and the rest, the defence is under a lot more pressure," he said.
"I first saw that new shape used consistently when the All Blacks played against Ireland last year. Ireland have got Andy Farrell as their defence coach and they use a fairly hard press.
"When I saw the All Blacks using that shape, I wasn't sure whether it was intentional or not. I said to Rassie that it may be something that they are working towards."
They had advanced their game when the sides drew in Wellington this year.
"When we played them in Wellington this year, they used it a lot more. The difference between that game against us and the one against Ireland was the improvement they had made within that system," he said.
He was referring to the 1-3-3-1 attacking shape that's been used by the All Blacks and other top teams over the past few years. The new shape of 1-2-3-2, however, is aimed at harnessing the outstanding mobility and handling skills of the All Blacks forwards.
"They're steadily improving in that system. They're still trying to find out where their skill sets fit into this new attacking style.
"I think that they're really beginning to understand the can of worms they're opening," he said.
Springbok No.8 Duane Vermeulen, who is playing his 50th Test for the side, was guarded when commenting on the matter.
"It is the World Cup. It's the first game of the tournament for both teams. They might bring something new to the table. We might try something different, too," he said.