The Premier League's top two clash at Stamford Bridge on Sunday with Chelsea taking a two-point lead into the game.
And despite having a midweek UEFA Champions League clash with Atletico Madrid to come, Lampard cannot help looking towards the weekend.
"I don't think anyone will need to work hard to get up for the United game, we all know it's coming. We'll try and put some space between us and them at the top," said Lampard.
"We're in good form, very good form and that shows in the results - but there's room for improvement. There always is.
"Any moment of slacking either on the training ground or in our preparations and that form will quickly go away. So we will keep trying to improve and, hopefully, can get even better
"If we can win, then we can open a gap - if we don't there's a danger Manchester United can close it.
"We have the Champions League in between, and then we will really start to think about United. It's an exciting time.
"We're top of the Premier League but know United will make it difficult for us.
"Psychologically I don't think those things like us being top matter when the big teams meet each other.
"Look at last week. There was only one winner in many people's minds at Anfield and yet Liverpool beat United.
"I don't think league position and form count for too much. I believe when those games come around it's all about the day."