Gareth Southgate’s preparations for England’s opening game at Euro 2024 have hit another complication after illness prevented John Stones from taking part in the squad’s first defensive session in training on Wednesday.

Stones is believed to have a sickness bug and was kept in his room away from his England teammates in an effort to stop any chance of the illness spreading.

Southgate, who has already left Harry Maguire at home because of a calf injury, has been dealing with various concerns in defence before his side play Serbia in their first match in Group C on Sunday. ­Maguire’s absence is a blow, Luke Shaw is still recovering from a hamstring tear and Stones required treatment on his right ankle after England’s defeat by Iceland last Friday.

The situation is not ideal for Southgate , who will hope Stones, the squad’s most experienced centre-back, will be well enough to return to training on Thursday. The Manchester City defender is certain to play against Serbia if he is fit and is likely to be partnered by Marc Guéhi, who started both of England’s warm-up matches.

But while Stones has quickly shaken off his ankle problem, it would have been preferable for him to be present in training as the defence looked ahead to shutting out Serbia’s Aleksandar Mitrovic. Lewis Dunk, the Brighton centre-back, will be pushing to start with Guéhi if Stones’s health does not improve before the weekend.

This is Dunk’s first tournament and he struggled during England’s friendlies against Belgium and Brazil in March. There was surprise when the 32-year-old was picked instead of Eric Dier in Southgate’s ­provisional training squad for Euro 2024 and some critics believed that he was fortunate to be selected over Jarrad Branthwaite in the final 26-man party.

Yet Dunk, who is confident that he has recovered from a knee injury that kept him out of Brighton’s final game of the season, will back himself to step up if Stones is absent. “I would hope so,” he said. “Of course. But you never know. There are a few days until Sunday and we’ll see what happens. I’m not here just for a holiday. I’m here to play games and win matches, and hopefully we can take the trophy home.”

Dunk is one of 12 players in the squad with no tournament experience. Southgate has had to adjust without Maguire, who has been a constant next to Stones in central defence. Dunk and Guéhi have a combined total of 17 caps and are untested at this level. The same applies to Ezri Konsa and Joe Gomez, the other centre-backs selected by Southgate.Yet Dunk was defiant when it was suggested that England’s defence could be vulnerable in Germany. “That is your opinion. Of course we are dismissing that. That is your opinion and you are entitled to it, but inside the dressing room and inside the camp we are as confident as ever. We wouldn’t be here if the manager didn’t think we could play for England.

“There’s still experience in the group. Of course there’s some inexperienced ones in a tournament situation but I’ve got the experienced ones to ask questions to and they’re more than happy to help me out and give me advice on anything. I’m an experienced professional now, 32 years old, so I’ve played a lot of games and once you cross the white line you’re just going to do everything you can to win.”

Dunk wears the armband for Brighton and is vocal during games. “That’s one of my strengths on the football pitch. Off the pitch I’m not the loudest or the most outspoken. I’m probably more of a reserved guy, but on the pitch I’m outspoken and I’m there to win. Me communicating helps everyone else, so that’s what I’ll do.”

Dunk has shaken off the error that led to Romelu Lukaku creating a goal for Youri Tielemans when England drew with Belgium in March. “That camp didn’t go as I would have liked,” he said. “There was a mistake leading to a goal, but that is football, isn’t it? Everyone makes mistakes. It is how you bounce back from that. I had to come back into the pre-camp and show as much as I could. After that mistake I felt I did all right. Football is a game of opinions and the one that matters is the manager of England.”