"We can control what we bring but we can't control what South Africa will bring - and they will bring plenty," Fox told Newstalk ZB's Tony Veitch. "Because they would got a fright against Wales - they probably would have thought that Wales would have been easier to turn over than they were.
"So while they would have been happy to be through, they would have been grumpier than we were. And a grumpy South African team is a dangerous team."
But Fox believed the All Blacks were ready to tackle that wounded beast, with their familiarity with Heyneke Meyer's side leaving Steve Hansen's men well aware of what would await them tomorrow.
"We know exactly what we'll get," Fox said. "You've got to deal with their physicality - that's the first thing. Because if you can't, you won't win. So you've got to match that at a minimum.
"We understand that because we've played them enough. You don't have to say much to our guys about playing South Africa, in terms of the physicality you need to meet, because they've been there enough. It won't be for the faint-hearted and there will be periods during the game when we're going to have to dig very deep."
Fox also thought the Springboks would hold no tactical surprises for the All Blacks, who had been training during the week of how to counter the South African kicking game. Compounding that approach would be the weather in London, with rain set to greet the teams and make for an even greater arm wrestle.
"We think they'll kick a lot of ball," Fox said. "They've tended to do that in the really big games, we're sure they'll do that against us, and it's likely to be a bit wet so that'll dictate that to a degree.
"We're going to have to put pressure on their set piece and make sure the ball they get is a bit rough, which puts pressure on their kickers. If they get good ball, then we've got to try put pressure on the kicker so they don't get time to kick the ball well. And if they do, we've got to be really good in the air and get back in numbers."
Being put on the back foot will be in marked contrast to the romp over France, but Fox insisted the All Blacks could still produce a great performance even if the game is a tussle as tight as many are predicting.
"Backing up a great performance is not an easy thing to do, so we've talked about that and said we can still have another great performance - it just might look a bit different.
"It'll be a very different game - we know that - and it might be a game that'll go down to the wire. But it can still be a great performance if we get the result right. Even if it's just one point."
