The Red Devils were among 12 clubs that last month signed up for the breakaway European Super League, which collapsed within 48 hours due to huge, unrelenting pressure.
Those plans brought anger against the already despised Glazer family to a new level, with fans congregating at Old Trafford to demand change ahead of their Premier League match against rivals Liverpool.
But hundreds of supporters got into the stadium and on to the pitch, leading to an initial unspecified delay to the 4.30pmkick-off.
The Premier League said that “the safety of everyone at Old Trafford is paramount” and confirmation came through from United at 5.35pm that the match had been postponed.
“Following discussion between the Police, the Premier League, Trafford Council and the clubs, our match against Liverpool has been postponed due to safety and security considerations around the protest today,” a club statement read.
“Discussions will now take place with the Premier League on a revised date for the fixture.
“Our fans are passionate about Manchester United, and we completely acknowledge the right to free expression and peaceful protest.
“However, we regret the disruption to the team and actions which put other fans, staff, and the police in danger.
“We thank the police for their support and will assist them in any subsequent investigations.”
The Premier League confirmed the collective decision to call off the game was taken with security and safety in mind.
“We understand and respect the strength of feeling but condemn all acts of violence, criminal damage and trespass, especially given the associated Covid-19 breaches,” a statement from the league said.
“Fans have many channels by which to make their views known, but the actions of a minority seen today have no justification.”
“We sympathise with the police and stewards who had to deal with a dangerous situation that should have no place in football. The rearrangement of the fixture will be communicated in due course.”
Liverpool - another founding member of the Super League - said they were in “full agreement with the decision to postpone” Sunday’s match at Old Trafford.
“It is our position that public safety must be the number one factor in any such decision, with the ability to provide a secure environment for the participants, staff and officials being a particular priority,” the Anfield club said.
“It was clearly not possible for this to be guaranteed today due to a situation which escalated rapidly.”
United manager Old Gunnar Solskjaer said it was important for fans’ voices to be heard in a “peaceful” manner and downplayed talk of the protest being a distraction to Sunday’s match.
Fans congregated on the Old Trafford forecourt an hour before the protest got under way at 2pm, while another group headed to the Lowry, the team hotel, in the city centre.
The hundreds outside the ground became several thousand by the time the protest started, with two firecrackers let off as fans began to march towards the Munich Tunnel with green and yellow smoke filling the air.
Red fences put in front of the East Stand did not last long as the handful of stewards were swiftly overawed and barriers toppled.
Footage soon emerged of hundreds of fans breaking into the stadium and onto the pitch, with corner flags held aloft and one supporter seen throwing a tripod from the pitchside interview zone.
A number of the protestors left the ground around 2.30pm, exiting the stadium complex by jumping down to the nearby canal paths or running out through the main gates.
Another group is understood to have got into the stadium shortly after, with a small batch of protestors seen leaving the just as the team line-ups at 3.30pm for a match that did not take place.
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