UEFA is likely to give the green light to a new Champions League format on Monday.
The expansion of European football's premier tournament to 36 teams operating within a meandering 'Swiss model' tops the agenda for UEFA's Executive Committee meeting.
The change has been earmarked to come into effect for the 2024-25 season.
Dublin's fate as a Euro 2020 host city could also be decided, with European football's governing body to provide an update on the twelve venues.
While the Champions League revamp is favoured by the big-wigs of the European Club Association, fans of some ECA clubs have voiced their concern regarding the changes.
One controversial element of the expansion is the proposal that four places among the 36 be held in reserve as a safety net for "historical clubs" that fail to qualify.
Fans Europe - a conglomerate of fans groups hailing from several European clubs - have penned an open letter of objection to the ECA.
The letter is co-signed by supporters groups from Real Madrid, Manchester United, Paris Saint-Germain, Arsenal, Ajax and Bayern Munich among others.
In it, they say, "We are writing to you on behalf of them and millions of others across the continent who you have chosen to ignore in your attempt to take over European football.
"Your plans to restructure the Champions League by increasing the number of games, introducing qualification based on past achievements and monopolising commercial rights present a serious threat to the entire game."
🗣 “We demand that you drop your reckless plans.”
✍️ Fans’ groups from clubs on the @ECAEurope Board have written an open letter to chairman Andrea Agnelli opposing #UCL reforms. FSE has signed the letter & fully supports their stance. #StopUCLReforms pic.twitter.com/lY7BQwu65L— FSE - Football Supporters Europe (@FansEurope) April 16, 2021
The fans add, "Instead of realising your supposed goal of 'building a successful, sustainable, and socially responsible football industry', you will only make the gap between the rich and the rest bigger, wreck domestic calendars and expect fans to sacrifice yet more time and money.
"All for the benefit of whom? A handful of already wealthy clubs, investment firms and sovereign funds, none of which have the legitimacy to decide how football should be run.
"Even most ECA members stand to lose out from the proposed reforms.
"Such a blatant power grab would be indefensible at the best of times, but at the height of a global pandemic, it is nothing more than crisis profiteering - not to mention a stark contrast to the solidarity displayed by fans."
Meanwhile, UEFA is likely to deliver a verdict on the Euro 2020 host cities unable to guarantee the presence of supporters.
As well as the Aviva Stadium, Bilbao and Munich could also have games removed.
The Irish government has been unable to offer UEFA assurances of a 25 per cent capacity for the Lansdowne Road venue.
Bilbao's roadblock is the Basque government, who are also unable to provide such guarantees.
However, Spain may not lose its slate of matches, with the Spanish Football Federation (RFEF) ready to replace Bilbao's San Mames stadium with Seville's Cartuja stadium.
Spain were due to play Poland, Sweden and Slovakia at the San Mames, but could be bound for the venue of Celtic's UEFA Cup final defeat to Jose Mourinho's Porto instead.
"For us as a national team and as a country we feel it is fundamental to remain as a host nation," RFEF president Luis Rubiales said.
"It's true that there's some difficulties in Bilbao but UEFA need to decide on that. For us, if they decide to remove it, it would be terrible for us if those games went to another country.
"I'm going to do everything that's in our powers in order for Spain to remain as a host nation and La Cartuja is a fantastic stadium that has everything it needs to host it.
"We have a relationship with the regional government and the stadium and so if this were to happen Seville would be our first choice, but it's not up to us.
"Hosting three national team games and a last-16 tie would be a big deal for us, both in terms of for fans and economically."
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