UEFA executive committee vice-president Giancarlo Abete has admitted that there is a chance of playing matches at Euro 2016 behind closed doors after yesterday's terror attacks in Brussels.
Over 30 people were killed and around 250 wounded by three blasts at an airport and metro station on Tuesday, four months after 130 were left dead by similar strikes in Paris.
The November attacks in the French capital may have been worse had so-called Islamic State bombers been able to enter the Stade de France as France and Germany contested an international friendly.
Concerns have been raised over the safety at all of this summer's finals in France and although UEFA has reaffirmed its safety plans, former Italian FA chief Abete is not ruling out the possibility of empty stadiums.
"Euro 2016 is the kind of event we can't delay or postpone," he told Radio 24. "We can't exclude the possibility of playing behind closed doors as we cannot exclude terrorism.
"If we talked about potentially cancellable games such as a friendly or a competitive match that could be moved to another date, obviously this would not be the case.
"But we are talking about games which are staged for June, where as today we are going through about a very urgent emergency."
Euro 2016 begins at the Stade de France on June 10 when the hosts take on Romania.