Molby wants a high tempo from Liverpool on Sunday.
Both sides head into the game on the back of 3-3 draws from midweek but Molby has written in his Liverpool Echo column that he thinks the home side will come out on top if both sides play to their best.
He said: "If both teams play as well as they can then Liverpool will win but we've only played well once at home under Jurgen Klopp and that was against Arsenal on Wednesday. Can we perform at that level again?
"We have to get at United from the off. Liverpool went right to the final whistle against Arsenal and we looked the fitter team.
"If we can find that kind of energy against United we can upset one or two of their players. Centre midfield is certainly an area where we can get at them.
"Playing at a high tempo can sometimes make up for a lack of quality."
A win for either side would be huge but Liverpool showed both their good and bad side in their midweek draw against Arsenal. They have shown they can trouble the best sides when they go forward but they really need to tighten up their defence, as at least two of Arsenal's three goals required little effort.
United found their scoring touch in midweek and could easily punish Liverpool, even if their lack of goals has been something that has been focussed on a lot so far this season.