Fergie or not, Man Utd won't be able to nullify Barca because they just don't have the players capable of doing it. There also isn't a 'book' on barca ie. A way you play to beat them. There is the ultra defensive tactic that Chelsea, inter, man utd and real have used in the CL but that's been for two-legged semis and again, Man Utd don't have the players capable of doing this. I could see them play like they do against arsenal but they would get caned doing so. They just can't afford to give barca that much time and space in their own half.