According to police, the officer sustained a “serious stab wound” to his face, which necessitated emergency medical care.
During the demonstrations, flares were set off, and bottles and barriers were hurled in defiance against Manchester United’s billionaire founders, the Glazers.
Demonstrators outside the Manchester United stadium were “highly violent and antagonistic against officers” before being pushed into the stadium by a mob of about 100 protesters, according to Greater Manchester Police (GMP).
According to the force, some United employees were forced to lock themselves in rooms while people scaled the stadium wall.
The “reckless and risky” behavior has been criticized by a senior officer.
“The behavior exhibited today by those at both Old Trafford and The Lowry Hotel was careless and dangerous,” Assistant Chief Constable Russ Jackson said.
“We appreciate the fervor with which many fans support their team, and we completely support the right to peaceful dissent. There were plans in motion to guarantee that this could continue safely, but it became apparent very quickly that all of those involved had no intention of doing so peacefully.
“To keep the chaos from worsening, we had to remove police from front-line policing and send in reinforcements from neighboring units.
“Bottles and walls were dropped, police were assaulted, and people climbed the stadium roof, putting themselves and officers in danger.”
The police are now on the lookout for those who are responsible for the assaults and chaos, and their superiors have vowed to press criminal charges.
“We have opened an inquiry, and we will be working closely with authorities to ensure that we determine the full circumstances underlying today’s incidents and convict those responsible,” ACC Jackson said.
Following their unsuccessful effort to form a breakaway European Super League in April, the anti-Glazer campaign has gained enormous traction in recent weeks.
According to GMP, over 1,000 people gathered at Old Trafford, with about 200 at The Lowry Hotel.