Shea Charles will be a late arrival into the Northern Ireland camp ahead of the Euro 2024 qualifiers against Denmark and Kazakhstan.
The 19-year-old is the only member of the international squad still playing domestic football as he is part of the Manchester City squad preparing for Saturday night's Champions League final against Inter Milan in Istanbul.
Michael O'Neill is hoping the midfielder will join up with the rest of the team in Belfast on Sunday as they prepare for the trip to Denmark ahead of next Friday night's game at the Parken Stadium.
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With some of the squad having finished their domestic season a month ago O'Neill reinforced the importance of of the recent training camp ahead of this doubleheader.
"The training camps have been vital otherwise the lads who play in the EFL, who weren't involved in the play-offs, would have been going into the games without having played in five weeks, or trained for five weeks," he said.
"That's a risk for injury and the level of performance they can get to is debatable at that point.
"I don't think you can play these games without putting the training camps in.
"We're probably a little more challenged than some of the bigger nations because their players tend to all stop at the one time.
"It's more difficult when some players have finished in the first week of May, some are staying and playing longer in Scotland or if they're in the play-offs or the Premier League.
"Then we have Shea, who we won't see until the first time on Sunday, probably as he'll be travelling with the Man City squad to the Champions League final.
"We need the camps otherwise we'd just be rolling the dice in terms of the level of performance we would get.
"We only started to play games in June towards the tail end of my international career.
"I remember we played a doubleheader in Latvia and Lithuania but we came home in between, it wasn't the way the schedule is now.
"We didn't have that basis of a training camp, we just turned up and we hoped we would be OK.
"Your responsibility was to keep yourself fit and hopefully you were able to go and play in the games.
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