Scientists have said the Euro 2020 final in London on Sunday will lead to a spike in Covid cases.
The warning comes as authorities in the UK capital urged fans to follow social distancing restrictions, despite the excitement of the Wembley showdown.
It is expected the stadium will remain at 75 per cent capacity for the final between England and Italy.
There were 64,950 fans inside Wembley for Wednesday's England v Denmark semi-final, and a similar number of fans are set to attend on Sunday.
Denis Kinane, an immunologist and co-founder of testing company Cignpost Diagnostics, said a rise in cases among men should be expected.
“It's that demographic, those football-loving, predominantly male individuals of a particular age group that we're now seeing a surge in,” he said.
“So, just as we unlock socially ... we're actually going to have a spike.”
Prof Keith Still from the University of Suffolk said: “I think the stadiums are being correctly managed ... [but] the fact that we've got the whole nation now celebrating – and rightly so, it's scary.”
Don't be too rowdy, police warn fans
London's Metropolitan Police on Friday warned fans they would intervene if behaviour goes “beyond what would be reasonable” on Sunday.
Laws preventing groups of more than six people gathering indoors remain in place in England until July 19.
“I think the big challenge has been large numbers of people gathering in breach of Covid regulations,” Deputy Assistant Commissioner Laurence Taylor told the Press Association.
“On occasions, behaviour goes a little bit beyond what would be reasonable. Wednesday was busy, lots of people around, lots of excitement. We fully anticipate Sunday to be even busier.”
Transport for London, the local government body responsible for the capital's transport network, advised the general public to avoid trains in the hours before and after the match.
Restrictions remain in place on the transport network for face coverings and social distancing, with fines of up to £6,400.
“Like everyone else in the country we are overjoyed that England has reached a first major final since 1966,” a spokesman for TfL said.
“It is fantastic to see such a level of solidarity across the nation. However, a small minority of people engaged in reckless and unacceptable behaviour [after Wednesday’s match], putting their lives and those of others at risk. We hope that we can all celebrate on Sunday and urge everyone to do so safely.”
Uefa said every spectator must also present a certificate showing they are double vaccinated or have recently tested negative for the virus
The football body also said there would be staggered entry for fans and 800 hand sanitiser units distributed throughout the stadium.
“We have been working diligently with the host associations and local authorities to ensure a safe and festive environment at the games,” Uefa president Aleksander Ceferin said.
Meanwhile, UK government has agreed to remove quarantine arrangements for 1,000 Italy fans.
Transport Secretary Grant Shapps defended the special arrangement on Friday
He said the fans would be on specially chartered flights, stay in London for only 12 hours, have a segregated zone at Wembley Stadium and return home after the match.
“They aren't able to travel anywhere else,” he told Sky News.