Atherton made history in September 2022 when he became the youngest senior footballer in the United Kingdom at 13 years and 329 days old, when he featured for Glenavon in the League Cup in Northern Ireland.

The 17-year-old moved from Glenavon, who he had been with since the age of four, to Chelsea's academy in July 2025 before signing a professional contract in October.

Atherton represented Northern Ireland at under-16 and under-17 level, and was a youth ambassador at the announcement in Nyon for the UK and Ireland's successful bid to host Euro 2028 in October 2023, but has now changed allegiance to the Republic of Ireland.

Speaking at his squad announcement for the World Cup play-off semi-final in Italy, O'Neill said "every player has the right to make that choice".

"He's a young player that had been initially in the Republic of Ireland set-up," he continued.

"He came back to be part of our set-up and I think Chris played maybe 17 times for representative teams for us.

"But every player has the right to make that choice, and obviously he's made that choice."

O'Neill also referenced the decision of Omari Kellyman, who is on loan at Cardiff City from Chelsea and switched to England from Northern Ireland in 2023.

Northern Ireland have also benefited from changes of allegiance, as Jamie Donley and Ronan Hale switched from England and the Republic of Ireland respectively in the past 12 months.

"We can't handcuff them to a decision that they made initially," O'Neill added.

"They have the right to make that choice once in their career, and Chris has decided to make that choice.

"We can only wish him well."