Van Gaal’s team’s 2-2 draw at West Brom on Monday has left them further in need of a positive result against Jose Mourinho’s side on Sunday.
It promises to be the biggest test of the Dutchman’s Old Trafford reign yet with United still to have faced any of last season’s top four.
But the former Netherlands and Barcelona coach remains relaxed and claimed his team’s title hopes are not over just yet.
“That’s possible but difficult to say because then I am arrogant,” he said. “But I have done it a lot of times.”
Van Gaal insisted his team’s failure to defeat West Brom did not mean their prospects against the unbeaten leaders should be dismissed.
“Now we have to play Chelsea, but you cannot compare West Bromwich Albion with great respect,” he said.
“I think Chelsea and (second placed) Man City are another level. We have to see if we can beat them.
“I am already thinking it starts with the offensive and also how the attackers are defending. You could see that in their (West Brom) first goal.”
United were forced to rely on Daley Blind’s 87th-minute equaliser to get a point in what was another reminder to van Gaal that his team remains very much a work in progress
West Brom had twice led through Stephane Sessegnon and Saido Berahino.
However, on each occasion they were pegged back with substitute Marouane Fellaini netting his first goal for the ‘Red Devils’ and Blind ensuring they at least stretched their unbeaten run to three matches.
Van Gaal rejected suggestions United should sacrifice flair for solidity.
“I don’t think that is the solution,” said the 63-year-old.
“I get asked this question a lot. You are right, today two errors, also in the past because I think we could have 8 points more.
“Then we are up there. But it is only a matter of time (until we get where we want to be). I believe in it.
“I think also football is made to be attractive for the fans and I think all of them enjoyed this as it was a great game.
“But it is two points lost. I think we were the better team and I am very disappointed by the result.
“We were two times behind but I don’t think West Bromwich Albion created too many chances.
“I have said to my players I cannot be happy. I am happy about our play style but not the result.”
As for Fellaini’s contribution, he added: “He was a very good substitute I think, but until now he is always injured and we have to build him up.”
West Brom were excellent value for their point following a display which provided further evidence they are progressing under head coach Alan Irvine.
“The players are massively disappointed having put in such a performance and coming so close,” said Irvine, who took over the job in the close season.
Leading scorer Berahino made it seven for the campaign as he gave England manager Roy Hodgson another reminder of his talents.
“Saido is in great form. He deserves what he is getting, his application has been really top class,” said Irvine.
“If he scores goals every week then he has a great chance (of a senior call) but Roy will decide when is the right time for him,” added the 56-year-old Scot.