Scotland, Wales and the Republic of Ireland have formally declared an interest in hosting Euro 2020.
Ahead of a midnight deadline, they have told Uefa that they would be interested in bidding to host the European Championships on a three-way basis.
Until now, Turkey were the only nation expected to bid.
But it appears that European football's governing body itself encouraged the joint bid from the Celtic nations, while Georgia have also now declared.
Turkey's bid is in some disarray already because its FA has been engulfed by allegations of corruption and match-fixing in domestic football, while it also conflicts with Istanbul's bid to land the Olympics in the same year.
A formal declaration of interest does not commit the Celtic countries to proceeding with a bid as a decision is not due to be taken by Uefa for 18 months.
Football Association of Wales chief executive Jonathan Ford stressed: "It is not a bid, it's a declaration of interest and that will allow us to obtain the information from Uefa so that we can fully assess and determine, independently and together, whether we should submit a bid."
The Celtic nations have a major hurdle to overcome to win the tournament, which has been expanded from 16 teams to 24 from 2016 onwards, should they decide to bid.
The competition's demands would mean the three nations might struggle to provide up to 10 stadia with sufficient capacity.
Scotland and Wales considered a joint bid for the 2016 championship - which will be played in France - before deciding not to go ahead, while a joint bid for Euro 2008 by the Scots and the Irish failed.
SFA chief executive Stewart Regan is reported as having told the website
"I'm not able to comment publicly at this stage because it has not gone to our board, but there will be an exchange of correspondence before the deadline.
"It's obviously something that has been discussed."
Asked if Scotland and Wales would be able to meet Uefa's criteria for stadia, Regan replied: "There are other ways of skinning a cat and alternative ways of being considered for a major tournament."
Uefa president Michel Platini has indicated his support for Turkey's bid - but only if Istanbul fails to land the 2020 Olympics.
Georgia have confirmed interest in hosting the tournament despite their hopes of Azerbaijan joining them in a joint bid being dashed.
Sports minister Lado Vardzelashvili told a news conference that they would proceed with a solo bid after Azerbaijan decided to concentrate on a bid by Baku for the 2020 Olympics.
"Azerbaijan has made a bid to host the Olympics, so Georgia will continue bidding for Euro 2020 independently," Vardzelashvili was quoted as saying by media in Georgia.
The former Soviet republic may struggle to fulfil the Uefa criteria for stadiums, but Vardzelashvili insisted that construction of "ultra-modern stadium" will start this year.