This afternoon's Premier League fixture at Old Trafford was postponed about an hour after the scheduled start time after a Man United fan protest breached stadium security.
Thousands of supporters had arranged to meet at around 2pm to protest against their American owners - the Glazers.
It marks the first time that a game in the Premier League has been called off due to fan protests.
Shortly after the start of the protest outside Old Trafford, the security of the stadium was breached with fans inside the stands and on the pitch, setting off flares and causing damage to amongst others audio-visual equipment.
Neither groups of players were at the stadium - a separate protest was taking place outside the Man United team hotel. Some of Man United's ground staff locked themselves in rooms at Old Trafford while they were waiting for police to secure the stadium.
Greater Manchester Police said:
"Those in the stadium were evicted by officers but outside on the forecourt, hostility grew with bottles and barriers being thrown at officers and horses.
"Two officers have been injured with one officer being attacked with a bottle and sustaining a significant slash wound to his face requiring emergency hospital treatment."
"The behaviour displayed by those at both Old Trafford and the Lowry Hotel was reckless and dangerous.
"We have launched an investigation and we will be working closely alongside partners to ensure we establish the full circumstances surrounding the events and prosecute those responsible."
The chairman of Greater Manchester Police Federation, Stu Berry, said his organisation's thoughts "are with our injured officers" and that it "will be seeking a review of Sunday's operational risk assessment and public order resources" for its members.
"We witnessed appalling scenes - police officers are not punchbags for people protesting for their cause.
"At the end of their shifts, hard-working police officers should be able to go home to their families in one piece. Not be rushed to hospital."
Liverpool agreed to the discussions with Man United, the Premier League and local police that the game should be postponed. In a statement from LFC, they added:
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.
It was clearly not possible for this to be guaranteed today due to a situation which escalated rapidly.
A win for Liverpool today would have ended Man United's slim chances of winning the league, but also saw the end of the reds reign as Champions.
The reds will now have to squeeze their final 5 games into an even tighter calendar - the league season ends later this month.