A defeat for the Anfield club will leave United 10 points clear with a game still to play - and that Fairclough argues will surely end any fading hopes the Reds have of snatching the title.
The Reds prepared for the crucial clash against Sir Alex Ferguson's Premier League and European champions with a 4-0 thrashing of Real Madrid in Tuesday's Champions League clash.
And if Liverpool can win this weekend, they will cut United's lead at the top to four points, albeit with Fergie's side still having a game in hand to play against Portsmouth.
Fairclough said: "It's huge in as much as if Liverpool do have any hope of still figuring in the title they have to win at Manchester United
"For most people they've lost it over the last week or two with dropping those points, but if Manchester United are going to slip up they've got to start losing games, they can't just draw games, and Liverpool have got to go there and be one of those teams that win.
"They (Liverpool) can win at Old Trafford, if they approach it right they have enough quality when they are all on their game. The problem is people can't have an off day if you're playing Manchester United. But with the likes of (Steven) Gerrard, (Fernando) Torres and (Xabi) Alonso we have quality in that direction."