The Cottagers head into the match against Sir Alex Ferguson's title-chasing side on the back of a last-gasp defeat at Aston Villa and last weekend's home thrashing by Swansea.
"You need a lot of belief in yourself to win there," the Dutchman said. "Look at Crystal Palace in the cup, they did ever so well. "My old team Ajax beat them and Blackburn have beaten them so that is the feeling you need. You need to feel you're in with a chance otherwise you may as well stay here in London."
He added: "Maybe it is [the biggest challenge in the Premier League] now because they are top of the league, but I can imagine over the last couple of years Chelsea were probably the number one in England.
"Then Man United won the league so it varies, but it is a big game. It is one of the biggest games for a club like Fulham, but even when you go to Chelsea or even Arsenal they are probably the same."
Tomorrow gives Jol another chance to secure a first victory over Manchester United as a manager.
Jol saw his side lose 5-0 at home to United in December and had failed to win in six previous attempts while in charge of Tottenham.
If the Cottagers are to spring a surprise in Manchester, Jol will have to find a way to keep United quiet.
Dimitar Berbatov and Michael Carrick are among those that could be involved for the Red Devils, players Jol knows well from his time at White Hart Lane.
"I think Berbatov has done at United what he did for Spurs, which is score goals," he said. "Of course it is at a different level, but overall he has done well even though it is difficult for him to get a regular spot in the team. For Carrick it is different. He was one of the last youngsters at West Ham and we got him for not a lot of money and he never looked back."
Source: PA
Source: PA