Indeed, the manager admitted 67-goal Keane might not make the opening game against Sweden in Paris on June 13.

Asked if the 35-year-old would be fit, O'Neill said: "He thinks that he could be. If it's not Sweden, he thinks he'll be fit for the second game. That's the thoughts at this minute. But I'm not a doctor.

"Robbie is the captain of the side, Robbie feels he is going to be fit. James McCarthy did a little bit of work today and there was a good improvement in that sense. That helps a lot.

"I'm not a soothsayer, but I think that there's a fairly decent chance that they are going to be okay. We have got a little bit of time.

"James came off in that last game, but he has played a lot of matches for Everton, obviously, he's a pretty fit lad anyway at the best of times, but like anything else, you'd like some time on the field.

"But we can organise games while we are out in France, we have a little bit of time if that's the case - and even before that because we have got a week's training to do here."

The pair will be given every opportunity to prove their fitness before the big kick-off, although O'Neill hinted that the safety net of being able to call up a replacement if a doctor adjudges an injury to be serious was at the back of his mind.

He said: "We have got a couple of injured players at this moment - Robbie Keane and James McCarthy - and while you want to be going in with some skilful players, you obviously need to balance that with players who are fit.

"But the rules state that if some players don't make it through, you have got a little bit of time, so who knows what might happen?

"But this is the 23 that we have chosen. I have gone with it now, that's my 23."

There was a seat on the plane too for 40-year-old keeper Shay Given, who had become Ireland's longest serving player earlier in the day having stretched his international career to 20 years and 65 days.

But that meant heartache for Davide Forde, who missed out along with Darron Gibson, Eunan O'Kane, David McGoldrick, Callum O'Dowda and Harry Arter, who suffered a thigh injury in training on Monday evening.

O'Neill admitted the decision-making process had been a difficult one.

He said: "I'll tell you why the decisions are tough - they are tough because these lads want to play for their country and that's the big issue.

"At club level, you can talk to players. It's an every week occurrence. I'm not saying it's always easy to leave players out, particularly when big games or big tournaments are around the corner, but at club level you feel as if you will see the player two days later, you might sit down and have a chat about it again.

"Some of these players will obviously leave the 23 tomorrow and that will be disappointing for them because they do want to play. They want to play for their country, they have got great pride in doing so.

"I'm not exaggerating that for the sake of it, but that's the difference between that and club level."