Declan Rice was forced to make a public apology on the eve of a potential England debut at Wembley after it emerged the West Ham midfielder had posted apparent support for the IRA on social media in 2015.

The midfielder was 16 and a member of the Republic of Ireland’s junior squads at the time of the Instagram comments in which he wrote “upthera” on one, and “my brudda. UP THE RA. Wait Till We Draw England” to a teammate on another.

Rice, born in Kingston upon Thames but whose paternal grandparents are from Cork, was a regular in Ireland’s junior teams and was capped three times by the senior side in friendlies. After much deliberation he switched his international allegiance to England last month.

“I am aware a poorly expressed comment I made when I was a junior player has been circulated on social media,” said Rice, who was named Ireland’s young player of the year last week. “I recognise now that my attempt to show support for my teammates at the time could be negatively interpreted. While my naive words were not meant to be a political opinion and do not represent who I am, I sincerely apologise for any offence caused.”

Gareth Southgate said the “uncanny” emergence of the posts would not affect Rice’s involvement against Czech Republic in England’s opening Euro 2020 qualifier on Friday, though the manager is expected to start with the more experienced pair of Jordan Henderson and Eric Dier in central midfield.

“He’s apologised,” said Southgate, conscious the FA has consistently appealed for England supporters not to engage in anti-IRA chants. “It’s not representative of what Declan believes and feels, and his views. And outside of that, the obvious point is that this was when he was 15 or 16 when he was engaged in a social conversation with friends. He’s explained how he views the world today and it’s difficult to know without speaking to him what the context of that was.

“It would be easy to comment on something without having all of the background and context. But our message doesn’t change and Declan’s statement is consistent with that, so we still would be against any of our supporters taking up that sort of stance and I don’t think anything changes from an FA or England point of view.”

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Southgate intended to speak to Rice on Thursday night, while the FA will write to the player and remind him of his responsibilities. “I understand it’s not a situation that should just be dismissed but, equally, the context, the period of time that’s passed and his age at the time are all relevant in how we should deal with it,” Southgate said. “He’s fitted in really well with the team. He’s looked excellent. There isn’t a player that has been in the squad who I would hesitate to start in the game.”

Jadon Sancho is likely to make his first competitive start against Czech Republic – ranked 44 in the world but without the Sevilla goalkeeper Tomas Vaclik and their captain, Borek Dockal – after Marcus Rashford became the sixth withdrawal. The striker has returned to Manchester United for treatment on an ankle injury that has prevented him training this week.

Chelsea’s Callum Hudson-Odoi, who has never started a Premier League game, may gain his first involvement off the bench as Southgate’s England side continue to develop.

Southgate has called up 71 players and used 56 in his 31 games in charge, and could add Aaron Wan-Bissaka to that number for Monday’s game against Montenegro in Podgorica with the Crystal Palace full-back on standby to link up if further injuries occur.

“When I’ve looked back over the two years [and seen] who has scored important goals or made important contributions at different times, the squad has had to evolve,” Southgate said. “Part of that has been looking at bringing younger players in but also that we’ve always had players missing, and you just have to adapt and adjust. There’s real competition for places. The squad feels bigger and, although we have lost a lot of players, we have found two more who will be able to fit in, no problem.”