About 200 supporters got into the stadium in anger towards the Glazers and the scheduled 4.30pm kick-off has been pushed back.
There are safety concerns following the break in and Manchester police will need to give the green light for the match to go ahead.
Both team line-ups were confirmed an hour before kick-off but a full sweep of the stadium is needed following the security breach and there is damage to the pitch.
The protests delayed the arrival of both teams to the ground.
Sky Sports reported just after 4pm that both teams were still stuck a their hotels and that their departure routes were blocked.
It is thought the Premier League’s Covid bio-secure bubble has been burst as the fans did not gain access to the dressing room, but there are concerns from a safety perspective.
There are thousands of fans outside the ground and some still inside.
Referee Michael Oliver, as well as former United captain Gary Neville, had their vehicles surrounded as they entered the stadium.
Those fans who gained access to Old Trafford did so via the Munich Tunnel after pushing down barriers, despite the attempts of security guards to prevent that happening.
If the game does go ahead, Manchester City could seal the title today.