Claudio Ranieri’s men are three points away from winning their first ever title and they travel to Manchester this weekend.
“We cannot allow them to become champions at Old Trafford,” Van Gaal said on Friday in his press conference.
“We won’t spoil their party, just postpone it a little.
“I was the first who said that they could be the champions, so for me it is not a surprise.
“I have seen it many, many times, I believe in team-building and this manager (Ranieri) has done that with this team.”
Van Gaal added: “They had the circumstances to play always with the same team and didn’t play as many matches as the other teams in the Premier League, so it’s possible, always possible.”