Republic of Ireland striker Jonathan Walters will miss Friday night's friendly against Switzerland with a hamstring strain. Ireland's player of the year returned to Stoke for treatment on the injury but could return to play a part against Slovakia next Tuesday.

Robbie Keane sat out training once again this morning, but manager Martin O'Neill is confident he will be available for both games.

Speaking after training, O’Neill once again refused to be drawn on his own future with talks over an extended deal — his current contract expires after the finals — expected to take place soon.

He said: “Loads of things can happen between now and then and there’s no point in turning around and telling you that there’s an absolute degree of certainty about anything. What we want to do is not only try to enjoy the Euros if it’s at all possible, but also try to make some sort of progress there as well, so we will see how things go. But who knows?”

O’Neill also said he would reluctantly accept playing Euro 2016 games behind closed doors if the ongoing terror threat meant that was the only alternative. Uefa insisted on Wednesday that it had no plans to keep supporters out of games at this summer’s finals in France in the wake of Tuesday’s attacks in Brussels.

However, O’Neill admitted that, should security officials decide that is the best solution to guarantee the safety of all involved, they would have to do it. He said: “If someone wants to make an attack as happened yesterday, it’s very, very difficult to deal with that, but overall the security that we’re being provided with is really excellent and like everything else, I’d comply with anything that is happening.

“There’s talk about matches being played behind closed doors, but the safety of people is of paramount importance and anything that is agreed upon, we will fall in line. If that is an alternative and it’s the only alternative, then if we are going to have the competition, we may have to comply with it.”

Heightened security around the tournament is likely to have repercussions for both Ireland and their fans around their base in Versailles, with the atmosphere unlikely to be as relaxed as it was in Sopot four years ago. O'Neill said: "The hotel that has been sorted out for us is actually very, very good. The possibility of players going into the town now might be a bit of an issue, whereas we though before that it looked really lovely.

“The town there, Versailles itself, is just really excellent, and it’s only a three, four, five-minute walk as well, so all of those things looked pretty good. If, of course, security is tightened as it probably will be, then maybe the players might have to stay closer to the hotel. I don’t think we want to turn away supporters, but at the same time security, I think people will realise that it might be very, very tight.”