The Blues have been in formidable form at the start of the campaign, and have dropped just two points in their eight matches.
Van Gaal has admitted that his side are behind Chelsea in terms of their consistency, but he is confident that they can inflict the first defeat of the season on Jose Mourinho's men at Old Trafford.
"You have to analyse that I have started just three months ago and he has been at Chelsea longer," Van Gaal told reporters.
"I have said that before. So it is logical that he's further with his team than I am with Manchester United. But, nevertheless, we can win on Sunday."
United are sixth in the Premier League going into the match against the Blues.