The venue for the Champions League final is expected to be confirmed on Thursday with Porto now the clear favourite.
The Portugese city looks likely to be the replacement venue for Istanbul due to Turkey being on the government's Covid-19 red-list for international travel, meaning the country should only be visited in exceptional circumstances and returnees to the UK must isolate in a government-approved hotel for 10 days.
Hopes of staging the all-English encounter between Manchester City and Chelsea on May 29 at Wembley appear to have faded after no agreement could be reached with Uefa on lifting the quarantine rules for 2,000 VIPs, staff and media to come to London.
The European governing body had been involved in talks with UK authorities this week over the possibility of switching the game to London but an agreement has not been reached.
It is understood the main sticking point in negotiations has been over the number of quarantine exemptions football's governing body has sought for sponsors, VIPs and broadcasters.
The government has so far been unable to agree to Uefa's requests.
However, appearing on ITV's Peston on Wednesday, Sport Secretary Oliver Dowden was hopeful that the final could still take place at Wembley.
Mr Dowden confirmed there"are a couple of issues" the government is still "working through" with Uefa, but he believed they had "removed all the barriers".
When asked by ITV News Political Editor Robert Peston whether the problems are to do with Covid quarantine periods, Mr Dowden said: "I mean Uefa want to bring a large number of people in without quarantine, now I understand why they have a desire to do that."
Mr Dowden said: "We do have to make sure that we protect our borders, so our scope for movement on that is very, very limited.
"But I'm still hopeful we may be able to get it here."
Amid the discussions, Portugal emerged as a potential alternative.
ITV News understands Porto is now in pole position, so long as Uefa receives clarity on entry restrictions and stadium capacity limits at the preferred venue of the Estádio do Dragão.
Uefa wants to know what will happen when current international travel restrictions in Portugal end on Sunday.
Its hope is that rules can be relaxed to allow fans to travel from England to Portugal.
Currently travel into Portugal from countries outside the European Union is only allowed in limited essential cases.
Fans would not face much hindrance returning to the UK, with Portugal currently on the government’s ‘green list’, meaning quarantine is not required once international travel from England is allowed to resume from Monday.
Uefa will also want to know how many spectators can attend the match.
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The Portuguese top flight announced on Wednesday that fans will be allowed to attend the final round of matches next week, but venues will be limited to 10% of capacity.
Uefa will clearly hope the Portuguese authorities will be prepared to allow a higher capacity for the final.
If satisfactory guarantees are received, a decision could be confirmed on Thursday.
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Both clubs are familiar with the Estadio do Dragao having played Porto during this season’s competition.
It would also be the second successive year that Portugal has stepped in to host the latter stages of the Champions League.
In 2020, Lisbon’s two main stadiums hosted all matches from the quarter-finals onwards in a rearranged mini-tournament.
One issue already confirmed is the team of officials for the final.
They are from Spain, with Antonio Miguel Mateu Lahoz chosen to referee the contest.
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