United sit eight points behind leaders Chelsea ahead of their trip on Saturday to Stamford Bridge, where victory for the visitors would see them right back in the title race.
Van Gaal does not expect to be crowned champions in his first season at Old Trafford, but has vowed to make Chelsea work hard in their final seven matches of the campaign, with Jose Mourinho's men also having a game in hand on the chasing pack.
"It is not logical [to win the league], but is possible," said the United boss. "It is more whens and ifs, and I don't believe in whens and ifs, I believe in facts.
"We are behind Chelsea but we have to play them, Arsenal do also, so we can lay pressure on Chelsea's shoulders, then you never know.
"We have seen in previous Premier League seasons [it has been done], so it is always possible, but it is not logical. I think that Chelsea will be satisfied with a draw."
