Behaviour expert Professor Stephen Reicher, of the University of St Andrews, said people gathering in homes and “forgetting restrictions” could be the problem – and not fans in stadiums.
The Sage subcommittee member said new data from Scotland shows the infection rate is now three times higher for young men.
In recent days, a gender gap has opened up after around two thirds of cases in the 15 to 44 age range have been male.
He told BBC Radio 4’s Today programme: “Actually, interestingly, I think the major problem with football is not people at the matches, it’s people at home not taking precautions.”
“I saw data yesterday from Scotland showing that whereas two or three weeks ago, the ratio of males and females, men and women, who get infections is roughly the same.
“Now it’s about three times higher for younger men, and the obvious explanation for that is people meeting up at home, forgetting restrictions.”
It comes as the total number testing positive in Scotland the past 24 hours hit nearly 3,000.
Under current restrictions, six people from three households can meet in homes in both Level 1 and Level 2, while stadiums and evets have allowed to reopen with certain numbers.
It means fans were allowed to watch Euro 2020 games at Hampden Stadium and some 20,000 Scots headed down to London to watch the Scotland vs England clash.
Prof Reicher said people had a right to feel confused by messaging from the government over restrictions.
He said: “The point is that 60,000 people at the match sends a message to 60 million, which is ‘well if they can all meet together why can’t we?
“I’f they’re rammed together and leaping up and down and hugging each other when a goal is scored, why shouldn’t we?’
“The most potent form of messaging, in fact, are the policies we put forward and we’ve got to think of those policies, not only in terms of what they do practically, but the types of messages they send and the ways in which they change behaviour.
“If we live in a society which tells us ‘well, it’s fine for 60,000 people to meet at Wembley’, it’s very hard at the same time to say to people, ‘look, there’s still a pandemic out there, and we’ve still got to be careful’.”