The chief of Greater Manchester Police says his force are "fearful" of crowds turning up at football stadiums if the Premier League season restarts.
The league hopes to return on 12 June with games played behind closed doors.
But GMP chief constable Ian Hopkins believes some "tricky fixtures" could pose a problem for policing.
"Liverpool coming to Manchester City I have no doubt would attract crowds whether they're allowed in the ground or not," he said.
"It needs very, very careful thinking through."
League leaders Liverpool were 25 points clear of reigning champions City when the Premier League was suspended because of the coronavirus pandemic on 13 March.
Hopkins added: "What we're fearful of is that people will turn up either at neutral grounds or at home grounds, and some of that could be particularly problematic.
"I'm not saying from a policing perspective it would be impossible to police because clearly it wouldn't - we police hundreds of thousands of people in normal circumstances at events right across Greater Manchester.
"But we are in very special and difficult times, and it remains a health issue so the thought of large groups of people coming together and not practising social distancing is a difficult one. We've all got to get to a position where we feel it can be done safely without jeopardising people's health and that has to be the starting point for people.
"The next point then is what provisions can the clubs put in place to prevent people coming, and obviously we can use legislation where it's applicable to stop that as well."
The Mayor of Greater Manchester, Andy Burnham, says the "best way to approach" resuming the season should be to consult with those "that would be most affected" - the players.
On Saturday, a third Brighton player tested positive for coronavirus, while Manchester City and Argentina striker Sergio Aguero has previously said players are "scared" about the prospect of returning to action amid the pandemic.
His City team-mate Raheem Sterling shared his concern on his YouTube channel on Monday, saying he feels "reserved" about playing.
"You have to take on board the concerns of the players and others have been speaking out in the last day or so and surely their views should be taken as a priority when it comes to any restart," said Burnham.
"It's about their health and safety and it's not being dictated to by television or by money and if players are not in a position where there's a clear feeling that they should return then there shouldn't be a return."
