England defence coach Kevin Sinfield said on Tuesday they are aware of South Africa's potential tactical surprises before this weekend's Rugby World Cup semifinal in Paris.

During last weekend's quarterfinal win over France, Springboks head coach Jacques Nienaber and his director of rugby Rassie Erasmus made a few maverick decisions.

They started with an inexperienced half-back partnership before bringing on 2019 World Cup-winning playmakers Faf de Klerk and Handre Pollard after just 45 minutes.

South Africa also chose to take a scrum from a free-kick in their own 22 as they continued to be innovative in knocking out hosts and favourites France.

This weekend's winners will face New Zealand, who beat Six Nations champions Ireland in the last eight, or Argentina in the final on 28 October.

"(It's) not just the curveballs, I just think how good they are," Sinfield told reporters of the challenge of playing South Africa.

"You tell me what part of the game is a weakness and I'd say something similar about the French, the Irish, even the All Blacks at the minute, the way they're playing.

"We understand this team are very, very smart, they are coached particularly well and they are right across the laws, they understand all the intricacies and we've got to be ready for whatever comes on Saturday evening."

Nienaber and Erasmus came into the Boks set-up in 2018 while Sinfield and England head coach Steve Borthwick have been in their positions for a matter of months.

England, champions in 2003 and runners-up to South Africa at the last World Cup, have played with a simple, unflashy gameplan which has led to them being the only unbeaten side left in the tournament.

"We're not at the point where we can try and find 0.01 per cents, we're not there," Sinfield said.

"Maybe in five years' time, this group might be in a position where it can start looking at those things but not at this moment in time."

"If we don't get our big blocks right on Saturday then we'll be blown away," the former England rugby league international added.

'GOOD MEN'

Before coming into his role with England, Sinfield spent a season under Borthwick at English Premiership club Leicester Tigers.

They helped the Tigers to the league title and Sinfield worked with three members of South Africa's squad, No 8 Jasper Wiese, forward Marco van Staden and fly-half Pollard at Welford Road.

"They're good guys, good men and great players," Sinfield said.

"I didn't work with Handre for that long, but Jasper and Marco van Staden, I loved working with both of them.

"We understand the strength in depth they've got."

One selection headache facing England on Saturday is whether to pick the creative Marcus Smith as a counter-attacking threat, or the reliable Freddie Steward to deal with the Boks' kicking game.

Smith was preferred to Steward for last Sunday's victory over Fiji

"He (Steward) is a great lad, you know what he is about, he works incredibly hard at his game, he cares and he is an unbelievable full-back too," Sinfield said.

"Just because Fred wasn't selected last week doesn't mean he does anything wrong.

"He has actually done a lot of great things and a lot of things right but Steve and the coaching team thought it was the right thing to go with Marcus."