Fin Smith is a major doubt for England’s clash with Ireland on Saturday with Marcus Smith ready to step into the breach for the penultimate round of the Guinness Six Nations.

Fin Smith was the solitary member of Steve Borthwick’s squad to miss training on Tuesday as he recovers from a calf injury and with only Thursday’s main session left before the Twickenham showdown, time is running out to prove his fitness.

The 21-year-old fly-half has won his first two caps in his breakthrough season for England, coming on as a replacement for George Ford against Italy and Scotland, but could now slip out of the 23.

“We have tried to look after him the last couple of days and we are hoping he will be in full training on Thursday. We are looking after him,” skills and kicking coach Kevin Sinfield said.

If Fin Smith is unable to convince Borthwick on Thursday that he is capable of facing Grand Slam-chasing Ireland, Marcus Smith is available to take his place on the bench.

The Harlequins player missed the first three rounds of the tournament, also because of calf damage, but could even challenge Ford for a place in the starting XV if Borthwick decides significant changes are needed in response to the 30-21 mauling by Scotland.

“Fly-half is a position where we have plenty of strength so Steve will make that call on Thursday after the session. If everyone comes through on Thursday, Steve has obviously got a headache,” Sinfield said.

“To have Marcus available having not had him available throughout the Six Nations is a big boost for everybody.

“Not only with what he brings on the field, but off the field as well. He has got some bounce about him, a big smile and he loves being out on the training field. He has had a big impact this week.

“He comes in and is himself all the time so we missed him in those first few weeks. I’ve loved working with him and he’s an incredible talent. He can play, that boy.”

Borthwick names his team on Thursday afternoon and England’s head coach will be hoping for a response after the backwards step taken at Murrayfield.

The most damning statistic to emerge from a fourth successive Calcutta Cup defeat was the 25 handling errors made, a staggering number that prevented their attack from functioning.

“That was an anomaly for us. We certainly haven’t seen that throughout training at all,” Sinfield said.

“We’ve worked particularly hard in trying to understand why it happened. Some of it is difficult to understand.

“When you’re trying to understand why someone’s dropped a ball, or someone’s thrown a pass without looking where the pass is going, there’s a bit more to it than the numbers.

“We’re trying to understand the people, what they are feeling and what they are seeing at that moment in time. So we’ve delved pretty deep into that.

“We put some balls down in the Scotland game, why that is we’ll never know for sure. But what we have to try to make sure is that it doesn’t happen again.”

England have revealed Marcus Smith could miss the entire Guinness Six Nations because of the calf injury that has ruled him of at least Saturday’s opener against Italy and Wales a week later.

A clearer picture over Smith’s fitness will emerge next week, but in the meantime veteran George Ford has been installed at fly-half for the Stadio Olimpico showdown with Fin Smith deputising from the bench.

Fin Smith is one of five uncapped players in the matchday 23 and should all of them get time on the field, it will be the highest number of new caps awarded in a single match since Stuart Lancaster’s first game in charge in 2012.

Centre Fraser Dingwall and flanker Ethan Roots are included in the starting XV while Smith, back row Chandler Cunningham-South and wing Immanuel Feyi-Waboso feature on the bench.

In a boost to England, Alex Mitchell has recovered from a leg wound to take his place at scrum-half, but the player who was expected to partner him at half-back faces an anxious wait to see if he will be involved at all over the coming weeks.

“Marcus will go back to England today (Thursday) and have further investigations later this week. He won’t be available next week,” Borthwick said.

“We’re not sure exactly when. Hopefully he will play in the latter part of the Six Nations, but it will be a number of weeks. We’ll know more next week.”

Mitchell’s immediate prospects of building on becoming first-choice scrum-half at the World Cup were thrown into doubt when he felt unwell as a result of the infected wound he took into England’s camp in Girona, preventing him from training fully until Thursday morning.

“Our medical team took great care of him over the weekend and at start of the week to get the infection under control and he looks brilliant,” Borthwick said.

“He played a lot of minutes for us during the World Cup and has played a lot of time for his club, so he is match sharp and ready to go. He looked fantastic in training today (Thursday).”

Experienced faces such as Ford, Joe Marler and Maro Itoje are present throughout the 23, but the rare inclusion of five debutants indicated the post-2023 World Cup rebuilding phase is under way, even if some of the picks were forced on Borthwick.

Dingwall starts at inside centre having been included in nine previous England squads without winning a cap, giving him the opportunity to prove he is the solution to the team’s problem position.

Although lacking the raw power of the injured Manu Tuilagi and Ollie Lawrence, the 24-year-old is a classy runner who is comfortable at 12 or 13.

Roots, a former jiu-jitsu champion who qualifies for England through his father, represented the Maori All Blacks but having left New Zealand in 2021 he has proved a hit at the Ospreys and now Exeter.

If Finn Smith, Cunningham-South and Immanuel Feyi-Waboso join them on the field, it will be an injection of fresh faces not seen for 12 years.

“Each one of those guys has earned his place in the matchday 23. Each one of them is an exciting young player,” Borthwick said.

“I didn’t think I’d be naming a 23 with five debutants. I’ve asked when the last time was England named a 23 with five new caps in it!”