The Daily Mail says United have adopted a siege mentality, with players sworn to secrecy over their preparations and staff given information on a need-to-know basis to avoid leaks and limit the security threat.
The club are trying to prevent a repeat of the scenes that caused the fixture to be postponed 11 days ago when protesters blocked the team from leaving the Lowry Hotel and hundreds more clashed with police at Old Trafford.
United are aware of the ongoing threat and have kept their plans a closely-guarded secret since then.
There will be tight security to prevent further disturbances after it became the first Premier League fixture to be called off due to a protest.
United have built a 10-foot wall and installed steel barriers to protect the most vulnerable areas of Old Trafford, including the corner of the stadium where fans twice broke in and got on to the pitch.
There was an increased police presence and more stewards on duty when United played Leicester, although the game against rivals Liverpool has always been considered a greater risk.