The 15-year-old is due to join Arsenal for their 2027/28 scholar intake after the Premier League champions agreed a deal with Larne during the summer. Blayney has also signed a pre-contract agreement to take up professional terms with the north London club.
His latest involvement with Northern Ireland represents another step in a rapid rise for the highly rated goalkeeper.
Blayney is regarded as one of the most promising players to emerge from Northern Ireland’s JD National Academy, which brings together elite players at Under-15 and Under-16 level.
O’Neill has placed a strong emphasis on youth development during his latest spell in charge and has identified Blayney and 15-year-old striker Michael Mulholland as players with significant potential.
The pair trained with the senior squad on Sunday and were presented with signed Northern Ireland shirts in recognition of their progress.
Blayney’s involvement came as Northern Ireland prepared for their Nations League meeting with Georgia. The senior side had made an unbeaten start to the campaign, winning away to Georgia and Ukraine before drawing 0-0 with Hungary at Windsor Park.
Northern Ireland entered the fixture top of Group B2 on seven points and without conceding in their first three matches. A clean sheet against Georgia would have extended their defensive run to its longest in nine years.
For Blayney, the experience provides an early glimpse of senior international football before he begins the next stage of his club career.
Arsenal’s decision to secure the goalkeeper so young reflects the reputation he has built at Larne and within Northern Irish football. His development will now be followed closely as he prepares to move into the English academy system.
The training opportunity also places Blayney among a new generation of Northern Irish youngsters being monitored by O’Neill as he looks to build greater depth around the senior squad.