New Zealand are sweating on the fitness of prop Tyrel Lomax in the wake of their record 35-7 loss to South Africa in a Rugby World Cup warm-up fixture at Twickenham on Friday, as coach Ian Foster looked for positives from their limp display.

The Springboks ran in five tries to one and were dominant in all facets of the game, especially up front with their powerful forwards, a worry for Foster as the All Blacks look ahead to the World Cup opener against hosts France in Paris on September 8.

It was the biggest loss in New Zealand's history, surpassing the 28-7 defeat by Australia in 1999.

"You couldn't help but be impressed with what they (South Africa) did, they really got stuck into us tonight," Foster told reporters.

"Their physicality and their set-piece was superb and they had a massive game at scrum and line-out time. That was a big difference."

An injury in the warm-up to fullback Willie le Roux saw the Boks add a seventh forward to their bench in the form of Kwagga Smith and with almost an entirely new pack in the second half they were able to dominate up front for the full 80 minutes.

"The (7-1) split certainly helped them," Foster said. "We went with 6-2 and we needed that because we had a few dings up front.

"Both teams put a lot into that game, it was a great spectacle. Two weeks out from a World Cup it is going to prepare both of us really well. It was a massive performance from South Africa and they deserve credit for it."

Lomax left the contest early in the first half with a deep cut to his leg and Foster said there was some concern over it.

"Lomax has quite a nasty cut. It is very significant and so we'll have to wait and see and cross our fingers on that," he added.

Despite the scoreline, Foster believed the game would be beneficial to his side as they head to France.

"I think both teams needed that game, we certainly did. We lost the cohesion when we were put under pressure, but I thought our defence in the first 20 minutes was outstanding and if we had more discipline in key areas we could have counter-punched.

"But they forced us into errors and that caused us problems."