Marcus Smith was ruled out of England’s World Cup semi-final against South Africa because of concussion, head coach Steve Borthwick has confirmed.

Smith has been replaced at full-back by Freddie Steward after he took a series of blows in the last-eight victory over Fiji that resulted in him finishing the match with a bandaged head and fat lip.

A tackle by wing Vinaya Habosi forced him to undergo an HIA which he passed, but he failed the subsequent return to play protocols and has been stood down for Saturday’s Stade de France showdown.

England have made two further changes to their starting XV with prop Joe Marler and lock George Martin coming in for Ellis Genge and Ollie Chessum respectively.

“Marcus was unavailable for selection due to the return to play protocols. He was ruled out earlier in the week,” Borthwick said.

“He took a knock in the game and passed the first parts of the HIA process, which meant he finished the game.

“Then there are subsequent parts of the HIA process and one part of that he did not pass. And then it was confirmed to me he was unavailable for selection.

“He is perfectly fine in terms of symptoms – he doesn’t feel anything. We’d expect him to be available for selection after this weekend. It’s right to reiterate that player welfare is critical and vital to us.”

Whether a fit Smith would have been retained at 15 is unknown, but it appears unlikely given the precision and variety of South Africa’s kicking game.

Smith offers a cutting edge in attack but Steward is one of the game’s most accomplished full-backs – ultra-dependable under the high ball, strong in defence and a key component of England’s kick-chase.

Captain Owen Farrell is aware of the aerial onslaught coming in Paris but is backing Steward to thrive.

“The thing about Freddie is everybody knows how good he is in the air, everybody knows what a fantastic player he is in general,” Farrell said.

“But it’s the want to do it, the want to be in those battles, the want to go and get the ball back for his team, the want to defuse what’s coming our way. He is one of the best in the world at it.

“The kicking game has been a massive weapon for South Africa for years and years now. They’ve progressed it and they go on with a lot of contestable kicks.

“We’ve done our work and we’ve come up with our plan to negate what we can from them but also looking to be able to attack ourselves.”

The adjustments to the tight five see Marler’s scrummaging prowess get him the nod ahead of Genge, with Borthwick noting that South Africa have the “best scrum in the world”.

Martin will bring physicality to the second row while Genge and Chessum will take their place in England’s answer to the ‘Bomb Squad’ – the heavyweight forward reinforcements that the Springboks summon from the bench.

South Africa this week rejected the suggestion that in their quarter-final victory over France they used HIAs to rotate forwards Mbongeni Mbonambi, Pieter-Steph Du Toit and Duane Vermeulen, enabling them to take a rest.

Director of rugby Rassie Erasmus has a reputation for taking an innovative approach to the laws and testing their boundaries, but Borthwick has faith in the officials to spot any mischief.

“We have got a match officials team that’s world class, led by Ben O’Keeffe,” Borthwick said.

“I am sure everybody around the pitch as well will have every bit of process in place. There is no issues there from our perspective.”