Further talks are planned with Uefa in a bid to convince European football’s governing body to stage the all-English showdown between Chelsea and Manchester City at Wembley.
But the UK’s failure to agree quarantine exemptions to media, staff and VIPs is threatening to see the May 29 showpiece moved to Lisbon or Porto instead.
The final was originally due to be played in Istanbul – but those plans were thrown into disarray when Turkey was placed on the UK’s foreign travel red-list, with fans of Chelsea and City told not to go.
Portugal is on the green list, which means supporters would not have to quarantine upon their return to this country.
But after growing confidence the final would be staged at Wembley in front of 22,500 fans, a failure to reach a breakthrough in talks yesterday thrust Portugal to the head of the queue.
Uefa ideally wanted a decision to be confirmed by today due to the limited amount of time reorganise the event.
Any alternative venue has to be one they are familiar with, which is why Wembley has been among the leading contenders.
But they are also aware of how well-equipped Portugal is to stage games at short-notice, with Lisbon used for the rearranged final stages of last season’s competition.
Around 2000 VIPs, media and staff would be required quarantine exemptions if Wembley is to host the match.
Uefa are eager to make a final decision as soon as possible, with preparations usually taking months to plan, due to hotels, transport and media arrangements.
They are already fighting against time with the final now less than three weeks away.
If the game is moved to Portugal it is believed as many as 6000 fans from each club could be able to attend.