Prof Graham Medley told the BBC there may need to be a "trade-off", with the re-opening of schools seen as a "priority" for children's wellbeing.
It came after England's chief medical officer said the country was "near the limit" of opening up society.
On Friday, the PM said further easing of the lockdown would be delayed.
Measures due to come in this weekend, including the reopening of casinos, bowling alleys, skating rinks and some close-contact services, as well as the return of indoor performances and pilots of large gatherings in sports venues and conference centres, would be postponed for at least a fortnight, Boris Johnson said.
The expansion of wedding receptions to allow up to 30 people was also put on hold.
Mr Johnson told a Downing Street press conference on Friday he needed to "squeeze the brake pedal" on easing restrictions, following a rise in coronavirus cases.
And England's chief medical officer, Prof Chris Whitty, warned the nation had "probably reached near the limit or the limits" of what can be done to reopen society, meaning trade-offs may be needed to allow pupils to return to classrooms next month as planned.
Mr Johnson has previously pledged that both primary and secondary schools in England will return in September "with full attendance".
Asked whether restrictions of other activities may be needed to allow schools to reopen as planned, Prof Medley, chairman of the Scientific Advisory Group for Emergencies (Sage) sub-group on pandemic modelling, told BBC Radio 4's Today programme: "I think that's quite possible.
"I think we're in a situation whereby most people think that opening schools is a priority for the health and wellbeing of children and that when we do that we are going to reconnect lots of households.
"And so actually, closing some of the other networks, some of the other activities may well be required to enable us to open schools.
"It might come down to a question of which do you trade off against each other, and then that's a matter of prioritising. Do we think pubs are more important than schools?"
Another Sage member, Prof Calum Semple, from the University of Liverpool, said there would probably be a second wave of the virus in October and "some hard decisions will need to be made about what restrictions need to be reintroduced".
"Whether that's potentially the pubs and the hospitality sector taking a hit in preference to education will be a political decision," he told the BBC.
But Allyson Pollock, a professor of Public Health at Newcastle University, described the idea of trade-offs as a "diversion" and said she did not think this was the right tactic to control the virus.
"We need to be much more confident that the government is playing its part and has a coherent testing strategy - which it doesn't have - that the test results are interpretable and that they're putting in the necessary public health and primary care measures," she said.
"And then we would not need to see these trade-offs."
Prof Medley, an academic at the London School of Hygiene and Tropical Medicine, said the rise in coronavirus infections appeared to be among younger people.
This meant it was likely there would not be the same increase in virus-related hospital admissions seen in March, he said.
Kirsty Drake is supposed to be getting married on 15 August - when the decision on easing restrictions again is due to be reviewed.
She had finalised plans this week for a small wedding reception, but now the restrictions mean she is unable to go ahead with the gathering.
"I'm a little bit emotional about it today," she says. "Everything is all up in the air again."
"What I don't understand is that if I wanted to now I could book six tables in a restaurant outside and sit and have a meal with those same group of people I've just got married with. We'd have to [socially distance] at the venue anyway.
"In our situation it would be safer to have a meal at the venue where we are due to get married."
Beauty salons are among those affected by the prime minister's announcement on Friday. They will no longer be able to restart facial treatments, such as eyelash, eyebrow and threading services this weekend.
Ampika Pickston, who owns a hair and beauty salon in Altrincham, Greater Manchester, said the news was "crushing" and "extremely damaging" to her business.
She said her salon had been forced to cancel more than 20 clients after the easing of restrictions was put on hold.
"A lot of people are angry because they don't understand the difference between why can you still come in to get your hair done or your nails done, get a body massage, yet you can't have a facial treatment done," she told BBC Breakfast.
"I've had some clients actually crying on the phone because they've been waiting so long to feel human again."
This week, new restrictions were announced for people in parts of northern England, including Greater Manchester, east Lancashire, and parts of West Yorkshire, after a spike in virus cases.
The rules include a ban on separate households meeting each other inside their homes and private gardens or mixing in pubs, restaurants and other hospitality venues.
Figures published by the Office for National Statistics (ONS) on Friday suggest infection rates in England are rising, with around 4,200 new infections a day - compared with 3,200 a week ago. However, the level of infection is still significantly lower than it was during the peak of the pandemic.
On Saturday a further 74 deaths were reported in the UK, taking the total number of people who have died after testing positive for the virus to 46,193. The latest government figures also showed 771 new cases had been confirmed.
Meanwhile, more than two million people shielding against coronavirus in most of England, Scotland and Northern Ireland can now leave their home and return to work.
However, Macmillan Cancer Support said people in the shielded group do not feel safe enough to leave their home and are having to "make the impossible choice" between their health and their job.
It comes as businesses that have furloughed staff during the pandemic must now start contributing to the government's job retention scheme.
Stop chasing the money and start chasing the passion.