The full squad will meet up up in Dublin on Sunday 28 May before flying to New York the next day ahead of the international friendly against Mexico on Thursday 1 June at MetLife Stadium. They will then return for the 'Three' International Friendly with Uruguay at The Aviva Stadium on Sunday 4 June. The international camp will close with the 2018 FIFA World Cup Qualifier against Austria in Dublin on Sunday 11 June.
O'Neill's men are currently second in Group D at the half-way stage of qualifying with 11 points from their five matches. They sit level on points with Serbia and four points clear of third-placed Wales ahead of the game against The Austrians. James McClean's strike just after half-time gave Ireland the points when the two sides met in Vienna last November.
John made his international debut back in March in the Republic's 1-0 friendly defeat to Iceland at The Aviva Stadium, having been on the bench for their World Cup Qualifying draw against Wales four days earlier. The Cork-born defender has also been been capped at Under-17, Under-19, and Under-21 level.
The 24-year-old enjoyed an impressive season in West London following his move from Gillingham last summer. In total, John made 37 appearances, scoring four goals, as The Bees recorded a third consecutive top ten finish in the Sky Bet Championship.