UEFA will decide on April 19 whether Dublin can proceed as a Euro 2020 host city this summer.
The Irish capital is due to host three group games and one last-16 tie but on Wednesday the Football Association of Ireland said it could not provide UEFA with assurances on fan numbers as it continues to deal with the coronavirus pandemic.
A final decision on how many of the original 12 hosts actually stage matches this summer will be taken by UEFA's executive committee on April 19, with Munich, Rome and Bilbao also asked to provide additional information by that date.
Dublin and Bilbao – due to host all the matches in Group E between them as well as one knockout round match apiece – appear to be the venues most in danger of losing out if guarantees cannot be provided.
The English Football Association has previously said it stands ready to host additional games if another host is deemed unsuitable for any reason by UEFA, and has committed to a 25 per cent capacity limit for the group games and last-16 tie to be played at Wembley.
UEFA said the FA was hoping to confirm a higher capacity for the semi-finals and final – reported to be at least 50 per cent which would equate to 45,000 fans in the London venue.
Eight cities have so far provided guarantees over spectators, with Glasgow's Hampden Park set to be 25 per cent full for the four matches it hosts.
Budapest has been the most ambitious so far and is targeting full capacity, subject to spectators fulfilling strict stadium entry requirements.
Ticket holders from overseas are also set to be allowed to come to matches in the Hungarian capital, UEFA said, provided they present proof of negative results from two Covid-19 tests performed in the five days preceding entry into the country or a certificate of previous Covid-19 infection valid within six months prior to entry into the country.
Three other venues – Baku, St Petersburg and Bucharest – are also planning to make ticket-holding fans exempt from standard entry restrictions provided they can prove they are negative for Covid-19 at point of entry.
UEFA said fans seeking a refund had until April 22 to apply, and that ballots would be held for matches which were oversubscribed based on the capacity limits set. Unsuccessful ticket holders would be notified in May and have their money refunded.
The sale of tickets reserved for the countries which qualified via the play-offs – including Scotland – will go on sale early next month, UEFA said.