Martin O'Neill says the Republic of Ireland "may have to comply" with Euro 2016 games being played behind closed doors if the ongoing terror threat meant that was the only alternative.
Uefa has no plans to keep fans out of games at the finals in France in the wake of Tuesday's attacks in Brussels.
However O'Neill said it will be up to security chiefs to find a solution to guarantee the safety of those involved.
"Anything that is agreed upon, we will fall in line," the manager said.
A spokesman for the Football Association of Ireland confirmed the organisation is engaged in an ongoing security process and would be guided by the experts.
Martin O'Neill says the security the Republic of Ireland are being provided with for Euro 2016 is "really excellent"
O'Neill said: "If someone wants to make an attack as happened yesterday, it's very, very difficult to deal with that.
"Overall the security that we're being provided with is really excellent.
"There's talk about matches being played behind closed doors.
"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.
"The safety of people is of paramount importance."
Players to stay close to base?
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, Poland, four years ago.
O'Neill said the team hotel was "actually very, very good".
"The possibility of players going into the town now might be a bit of an issue," he said.
"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, I think people will realise that it [security] might be very, very tight."
O'Neill refused to be drawn on his own future with talks over an extended deal expected to take place soon. His current contract expires after the finals.
"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," he said.
"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?"