The odds on what was shaping up to be the most evenly poised match of this Six Nations took a sudden lurch after the Ireland captain, Johnny Sexton, was ruled out of Saturday’s game against France with a hamstring strain.

Sexton suffered the injury in training on Wednesday. Ireland have replaced him with the Munster fly-half Joey Carbery, and made James Ryan captain. The head coach, Andy Farrell, tried to make the best of the situation but, much as he insisted otherwise, there was an unavoidable sense that in a match that promises to be as tight as this one, the loss of Sexton’s skill, leadership and experience might make all the difference.

“That’s the sport we love, there’s always twists and turns, especially in the Six Nations,” said Farrell. “It’s a long old competition so there’s always going to be things we have to deal with. Johnny is an important member of the group, as a captain he’s integral to how we push forward, but at the same time this is about the group. It is not just about one player, it never has been, never will be.”

The 26-year-old Carbery has played 28 Tests, but has had such dismal luck with injuries that this will be the first time he’s started a Six Nations match. “I’m really excited,” he said. “I feel like I’m ready to go mentally and physically.”

Otherwise, Ireland’s starting XV is unchanged from their 29-7 win over Wales last weekend. Iain Henderson and Robbie Henshaw come on to the bench, as does the fly-half Jack Carty.

France have been forced into making one change, with the 21-year-old Yoram Moefana replacing the injured Jonathan Danty at inside centre. They have also swapped François Cros for Dylan Cretin in the back row. In a clear and ominous sign of their intentions, their head coach, Fabien Galthié, has loaded his bench with six forwards. France have been able to overpower Ireland up front before, and Galthié is planning on doing it again.

“We’ve fallen into that trap before against big physical sides when we’ve not been composed enough to play our game, so we’ve learned some lessons from that. We’ve got to play our own game, that’s the way we’re thinking. We’ve got to be brave enough to play the way we want to play, and not get distracted by thoughts like that,” Farrell said.

“We know the size of their pack, we know how good they are at the set piece, and we know how dynamic they are when they get into your 22, so their 6-2 split doesn’t really change anything for us.” He is doing his best to present the situation, Sexton’s injury and all, as exactly the sort of challenge his team wants to face.

That is certainly true for Carbery, who made his debut in 2016 but has spent years since on the sidelines. The ankle injury he suffered in the 2019 World Cup meant he missed a year. Since he came back last summer, however, he has helped Ireland to their famous 29-20 victory over the All Blacks last November, and started their 53-7 thrashing of Argentina a week later. “Anyone who’s been through a long-term injury knows how difficult it is,” Carbery said. “It makes you enjoy the good things in life, so I’m just delighted to be back playing, to be out there injury-free, and relishing playing in such a big game. Having gone through that I’m mentally stronger for it.”

“Joey is one hell of a player,” said Farrell. “He’s had a good solid two and half weeks in training with us and he knows exactly how we want to play, and we expect him to deliver like everyone else.” In a sign of just how important Sexton is to Ireland, he will still travel to Paris with the team. Farrell expects him to recover from the injury in “seven to 10 days”. In the meantime, Ireland will try and answer a question they’ve been wrestling with for years: how they’ll cope without him.