Euro 2020 is due to start in 100 days, on June 11, with Italy scheduled to face Turkey in Rome in the first game of a tournament that was postponed last year as a result of the COVID-19 pandemic. But with the vast majority of European countries under strict lockdown measures, UEFA has yet to decide precisely how, and where, the delayed Euro 2020 will take place.

The original plan of a 24-team competition in 12 different cities across the continent, from Dublin, Ireland in the west to Baku, Azerbaijan in the east, remains in place, but question marks loom large over many aspects of the 51-game European showpiece.

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A final decision on the format of Euro 2020 will be made at the UEFA Congress in Switzerland on Apr 20. Here's what we know, and what we still don't, about this summer's flagship competition.

With additional reporting from Stephan Uersfeld and Julien Laurens

Are the Euros certain to take place?

Yes. The worst-case scenario is a tournament played in a secure bubble with no fans allowed inside stadiums, mirroring the format used last August to conclude the Champions League and Europa League in Portugal and Germany, respectively.

From a financial perspective, many of UEFA's 55 member nations depend on the funds generated by the quadrennial championships. UEFA is committed to all 55 receiving the revenue agreed upon in 2018. As such, €371 million in prize money is at stake for the 24 nations that qualified, while another €775m will be distributed to all the member associations over the next four years. UEFA is using its reserves to pay the bill, so the money generated by broadcasting and sponsorship revenue (Editor's Note: ESPN is a rights holder for the Euros) will be crucial and a big reason why Euro 2020 will go ahead.

It's scheduled to start on June 11. What will it look like?

That's the big question. As reported by ESPN on Jan. 8, UEFA were considering three options: Plan A was the original blueprint with stadiums full of fans up to 70 percent capacity; Plan B focused on 30 percent capacity; Plan C was one nation hosting a tournament inside a bubble.

Two months on, the picture has changed. A mid-winter surge in COVID-19 infections throughout Europe has led to uncertainty over whether governments will allow games to take place in their cities come June and July.

It means that a Plan D is now in play, which revolves around the tournament being staged in fewer cities -- potentially those willing to allow some fans in stadiums. As yet, no city or country has pulled out, but sources have told ESPN that the appetite to host games is waning in Dublin and Bucharest.

Surely there are concerns about a pan-European event in 12 cities during a pandemic?

Within the game, executives, coaches, and players are planning for a 12-city tournament, but there's a sense of confusion and concern about the likelihood of it going ahead in the original format. In February, Champions League and Europa League matches were moved from their original "home" locations to neutral venues because of differing COVID-19 protocols -- Arsenal and Benfica played their last-32 fixtures in Rome and Athens, for example -- while travel between some nations is prohibited. For instance, the UK is not allowing any travel to or from Portugal at present.

In short, football is at the mercy of the pandemic and governments could veto games on their soil.

This isn't just about UEFA then?

No. Every major tournament requires the support of the host government. That's complicated enough, but UEFA are working with 12 different national administrations -- with differing infection and vaccination rates -- to make Euro 2020 happen.

Some host nations have started to relax their COVID-19 restrictions, while others have extended them. There are also political issues at play, with governments having to assess the public desire to stage Euro 2020 games in the absence of travelling fans. It's still unclear whether some governments will allow fans to cross borders.

When are UEFA going to make a final decision on the format of tournament?

Initially, UEFA had hoped to finalise details in early March in order to allow national associations, governments, broadcast partners, and fans enough time to adjust to any changes, but the second wave of COVID-19 has prompted a further delay. UEFA will confirm the Euro 2020 format at Congress on Apr. 20, seven weeks before the tournament is scheduled to begin.

Sources have told ESPN that although the situation across Europe will be unclear by then, UEFA president Aleksander Ceferin is determined to make a decision with as much up-to-date information as possible.

Is it possible that the tournament will be staged in one country?

It's unlikely, but yes, it remains a possibility. That said, finding a suitable host would prove problematic.

Which countries could be considered to be "in the running" for hosting?

According to sources, England, Germany, France and Russia are the realistic options because of the need to be able to accommodate and provide training bases for 24 teams.

England has the stadia, training grounds, and hotel network. Sources have said that the tournament could even be held solely in London at grounds like Wembley, the Emirates, Stamford Bridge, the London Stadium, and the Tottenham Hotspur Stadium. UK prime minister Boris Johnson claimed Tuesday that England is willing to step in and host additional matches, but sources have also told ESPN that, in the wake of Brexit, UEFA would be under intense political pressure to avoid a scenario in which Europe's major football tournament is being rescued by the London government.

There is a similar political issue with Russia. With modern stadiums built for the 2018 World Cup, Russia could comfortably host. But with the country banned from all major sporting events for two years by the World Anti-Doping Agency (WADA) because of a doping scandal, UEFA would be unlikely to risk the negative publicity.

Germany has little appetite to take on the responsibility. In public, no one has spoken out against hosting the tournament, but there's little in the way of support. The Social Democratic Party (SPD), one of Germany's two governing parties, said in a statement earlier this month that the idea of Euro 2020 in its current format is "not convincing" and that "a tight territorial region, no fans and a good hygiene concept would be desirable [in order to allow] the tournament to go through."

Meanwhile Philipp Lahm, the former Bayern and Germany legend serving as the German FA's ambassador for their Euro 2024 hosting bid, ruled it out. "Currently, this is absolutely no scenario, I can clearly say that," he told Sportbuzzer. "No one can predict what will happen in the coming months, but right now it's open to debate that Germany will stage the tournament alone."

France has also made no moves to step in. A source told ESPN that even before the French Football Federation (FFF) could raise the possibility of hosting, the government said there was no chance of them approving it, not least after the logistics of organizing and hosting the 2019 Women's World Cup. The specter of presidential elections this year are a further obstacle.

Meanwhile, Gabriele Gravina, president of Italy's national football association (FIGC, or Federazione Italiana Giuoco Calcio) contradicted talk of a single nation hosting the tournament. "These are unfounded rumours, we have a lot of confidence in our government authorities and we are convinced that we will catch up with the vaccination policy. We are confident. We are ready for the kick-off of our first match in Rome."

What about the players? Are they going to be in bubbles throughout the tournament?

Unless the COVID-19 infection across Europe drops dramatically between now and June and allows for unrestricted movement, all competing squads are likely to have to adhere to the same regulations that have been in place in the club game since football returned last summer. Sources have said that it is highly likely that teams will be in bubbles for the duration of the tournament, with regular testing of players, coaches and officials.

Will UEFA push for players to be vaccinated?

Sources have said it is "very doubtful" that UEFA will insist on players being vaccinated, although the organisation is still to agree a confirmed position on this. A person familiar with the discussions told ESPN that UEFA will take a similar view to the Premier League, which has adopted a "wait our turn" position on vaccines. The UK government has been rolling out the vaccine to the population on the basis of age and vulnerability.

Any plans in place in the event of an outbreak / new wave of infections during the tournament?

UEFA has yet to draft a protocol that would cater for the impact of a potential COVID-19 outbreak in the summer, but sources have said it's likely to follow a similar format to the protocol used in the Champions League and Europa League. In those competitions, a suitable alternative venue is identified if a game cannot take place as originally planned. In the Champions League Round of 16, RB Leipzig's home game against Liverpool was moved to Budapest, while Atletico Madrid staged their home fixture against Chelsea in Bucharest.

UEFA are confident that any localised outbreak would not affect the whole tournament.

How about fans inside stadiums? Will that happen?

It's increasingly likely that fans will be able to watch games inside stadiums in some venues. Up to 10,000 fans will be allowed back into football stadiums in England starting May 17 and, according to government plans, all restrictions on numbers will be lifted on Jun. 21, which raises the prospect of Wembley hosting up to 90,000 fans for some games. However, sources tell ESPN that it's extremely unlikely.

While England is making progress towards fans returning, sources have told ESPN that fans won't be allowed to attend games in Ireland until September, suggesting that Dublin's four games at Euro 2020 will be played behind closed doors at the Aviva Stadium. Yet Jonathan Hill, CEO of the Football Association of Ireland (FAI), said this weekend that they were briefed by UEFA over the weekend on the topic.

"UEFA wants to see fans in all 12 of the stadia and all 12 of the cities, and we are planning on the basis that we will have fans in the Aviva Stadium," said Hill. That is the current situation, and that is the plan. It's now a situation whereby all 12 of the cities are working with UEFA and their governments to work out how many fans they can get safely into their individual stadia. In reality, we're all learning from each other in terms of the approaches that are being taken."

In Germany, the goal is to further reopen once the country goes under 35 infections per 100,000 for a seven-day period. Protocols in France are still strict, with a national curfew in effect and strict closure rules for hotels and restaurants. There are also no plans to welcome fans back to sporting events until after the summer. (Some discussions of hosting test events in Lyon, among other cities, won't be happening with fans in stadiums for a "few weeks," according to Sports minister Roxana Maracineanu.)

Jonathan Hill, CEO of the Football Association of Ireland (FAI), said over the weekend that they were briefed by UEFA on the topic of allowing fans at games. "UEFA wants to see fans in all 12 of the stadia and all 12 of the cities, and we are planning on the basis that we will have fans in the Aviva Stadium. That is the current situation, and that is the plan.

"It is now a situation whereby all 12 of the cities are working with UEFA and their governments to work out how many fans they can get safely into their individual stadia. In reality, we're all learning from each other in terms of the approaches that are being taken.

By mid-April, UEFA expects to know which countries will allow fans and which will not, and that could be a factor in deciding whether cities drop out or continue as hosts.

UEFA have already sold 90 percent of tickets for a tournament with fans. How will they resolve that?

This is a headache for UEFA, although cancellations and refunds are a strong possibility because of the likelihood of games being played in front of vastly reduced crowds. One option: UEFA could resell tickets to fans in local markets, but there's still no certainty as to how many fans will be able to attend in each city. The most likely scenario is for crowd limits to be set in April and tickets sold accordingly.

Will fans be able to travel?

Once again, this is dependent on the border policies of the current 12 host nations. Some may allow travel by June and July, others may not.

Sources have told ESPN that Euro 2020 will almost certainly be played out in front of domestic crowds, with no supporters able to travel from outside countries.