Football fans have warned that plans to exclude supporters who are not fully vaccinated against coronavirus from attending Premier League matches from October could cause "chaos" at some clubs.
Chairman of the Football Supporters' Association Malcolm Clarke warned the proposal being considered by the Government to make vaccine passports mandatory for events with more than 20,000 attendees will need to be "managed very carefully".
Prime Minister Boris Johnson was also facing further criticism from backbench Conservatives who were already opposed to plans to introduce their use for entry into nightclubs this autumn.
Talks are in an early phase with the Premier League to discuss whether supporters who have not been double-jabbed could be barred from entry, the PA news agency understands.
The use of vaccine passports could also be extended to lower divisions and other sports in England as ministers seek to reduce the surge of Covid-19 cases as other restrictions are ended.
While no final decisions have been made, it is being discussed whether vaccine passports could be introduced for seated events with a capacity of 20,000 people and over.
In unseated events such as music gigs, where there are greater concerns about strangers mingling and spreading Covid-19, the threshold for their introduction could be as low as 5,000 attendees.
Clarke, whose organisation says it represents more than 500,000 members, warned that some football fans may stop attending matches "unless this is managed very carefully".
"I think if they're going to do this with big football crowds then they need to have the resources to do the checks. I'm not convinced that all football clubs will be able to manage that in a way that doesn't cause some chaos," he told Times Radio.
"There will certainly be some football supporters for whom this will be an incentive, who are desperate to get back in the ground and watch their teams.
"There may be others who will say 'you know what, I've got used to being without going to the games and this is the last straw, I'm not coming back'. How it breaks down between those two groups and everything in between, I wouldn't like to predict."
The Prime Minister sparked a backlash when he made the nightclubs announcement on Monday, as he ended most of England's remaining coronavirus restrictions and allowed the venues to reopen for the first time since March last year.
He said vaccine passports could also be made a condition of entry for "other venues where large crowds gather", adding: "Proof of a negative test will no longer be sufficient."
Whether recent negative tests could allow entry to football matches was one area said to be still under discussion.
On Saturday night, a Government source said: "It's important that fans can continue to watch sporting events over the autumn, which is why we're exploring the role vaccines might play in this.
"This will not only allow full-capacity stadiums but has the added bonus of incentivising people of all ages to go and get their jab."
Shadow sports secretary Jo Stevens said Labour opposes denying access on Covid vaccination status alone, without the use of tests, which the party argues would be "more efficient".
"To insist on vaccine passports less than a month before the start of the season will cause major disruptions, especially for clubs at the lower end of the pyramid," she added.
Making their use mandatory in the Premier League from October, however, would give time to phase in their use with the season starting on August 14.
The English Football League declined to comment, but it is understood contingency plans have been under discussion in case the Government advised the use of vaccine passports.
But Mr Johnson would face a battle to get legislation mandating their use through the Commons, with many backbench Tories also vehemently against them.
On Sunday, senior Conservative Tom Tugendhat, the chair of the Foreign Affairs committee who has so far been supporting of coronavirus laws, said: "Vaccine passports risk a social credit system of control.
"If we need a vaccine for events like a party conference or a nightclub – why not to travel by a train, or go to a university lecture or a shop? What other choices will result in denial of service?"
Chief scientific adviser Sir Patrick Vallance has warned nightclubs have the potential to cause "super-spreading events", but it is unclear to what extent what role football matches have in spreading Covid-19.
There were concerns, however, around fans travelling to London during Euro 2020 after Public Health Scotland figures showed there were nearly 1,300 Covid-19 cases linked to fans at events as Scotland faced England in the group stages.
That included 397 people who attended the clash in Wembley on June 18, according to the official figures.
