Smith was among a number of players placed on modified training as preparations began for the match at the Stade de France, but England are cautiously optimistic he can win his fitness battle.

The 24-year-old ended the quarter-final victory over Fiji with a fat upper lip and a bandage on his head after he was the victim of a dangerous tackle by wing Vinaya Harbosi, forcing him to depart for an HIA which he passed.

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The Harlequins player, who has been moved from his accustomed position of fly-half for the World Cup, defended bravely on a tense evening at Stade Velodrome and is contention to retain the number 15 jersey ahead of Freddie Steward.

Defence coach Sinfield insists a clearer picture of his availability will emerge over the coming days after he was joined by Jonny May, Manu Tuilagi, Tom Curry, Courtney Lawes and Dan Cole in missing the start of Tuesday's session.

"Marcus is good. He's one of those who have been modified [on Tuesday] so we'll get a clearer read in the week, but fingers crossed he will be good to go," Sinfield said.

Sinfield: Being 'outsiders' gives England extra motivation

Regardless of whether Smith manages to recover in time, South Africa are strong favourites to get the win in Paris.

England were almost completely written off by most coming into the World Cup after a poor Six Nations campaign was then exacerbated by a shock defeat to Fiji in the run-up to the tournament.

Having laid those ghosts to rest, Defensive coach Sinfield is now confident England can use that lack of expectation and pressure to their advantage on Saturday evening.

"We were thought of as outsiders back in August - we took it on the chin," he said.

"I think throughout this five or six weeks together, we've made huge improvements and we know we need to be hugely improved again at the weekend. To get the job done.

"Some guys will use it at motivation but I think others will want to win because they want to win, so there's probably a mix of personalities and motivations, whether it's through fear or joy, you get a mixture of the two.

"I think the individuals will know which buttons they need to press for themselves.

"They've worked incredibly hard this last 19 weeks and I look forward to watching them go on Saturday."

Sinfield is under no illusions about the size of the challenge and believes the tournament's defending champions play "the best rugby" but reckons England have enough about them to pull off a shock victory against the Springboks.

Steve Borthwick's side had to survive an incredible late fightback from Fiji at the Stade Velodrome in Marseille on Sunday to make it into their sixth Rugby World Cup semi-final and had Owen Farrell's boot to thank for helping to secure an eventual 30-24 victory and a last-four berth.

Now though, after five wins out of five in the competition, comes the toughest assignment yet.

"We knew it'll be a tough challenge, especially with the draw," said Sinfield. "It was either the hosts [France] or the current holders and we have the upmost respect for them, we think they are a nation that play the best rugby and play some great rugby.

"They know what they are about and they don't shy away from it, and we look forward to the test at the weekend.

"I think we've had some physical challenges already this World Cup. We do appreciate, having watched the game at the weekend, what they will bring.

"There's some guys in our team that have had the experience of playing them before.

"But also, we've got some physical guys as well, and we understand that it's a big part of the game."

Chessum: They've got some unbelievable players in their pack

Leicester lock Ollie Chessum will form part of the England pack trying to overpower the Springboks unit at the Stade de France on Saturday.

Like his coach, he recognises the challenge England face in trying to do so and believes it will come down to whether England can execute on the day.

"These are the games you want to be a part of against the biggest teams on the biggest stage in the biggest competitions," said Chessum. "They've got some unbelievable players in their pack that bring an exceptional level of physicality and it's up to us to go out there that weekend and compete against that.

"Week-in and week-out we've grown as a group and got better in various aspects of our game. South Africa are unbelievable across the board and so we've got to try and be the same, if not better. We're hoping that we bring the physicality but we bring that level of execution with it as well at the weekend."

Follow England's Rugby World Cup semi-final against South Africa across Sky Sports' digital platforms from 7.30pm on Saturday (kick-off 8pm).