Chelsea are just four points ahead of Sir Alex Ferguson's men, who also have two games in hand. The Blues have played the other members of the big four at home this season but have only one point to show for it, from when they drew against United.
But defender Jose Bosingwa said the squad have been showing their determination to improve on that record in training all week and have a plan in store to stop Cristiano Ronaldo.
Bosingwa said: "This week I have noticed a greater intensity in training at Chelsea. I have seen more energy in all my colleagues because we have a big match against United on Sunday which is vital for the League title and we want to win it.
"Some people are beginning to doubt our chances for the title but we want to leave Manchester proving that there is a lot still be to be decided.
"To stop Cristiano is not easy but at Chelsea there are people who know him well, including the manager — we know what to do stop him