Both nations are already assured of their place in the next round, but would likely avoid hosts Brazil in the last 16 by winning Monday's match and topping Group B.
And, while giving a positive assessment of his charges' performance so far, Van Gaal knows he needs to be wary of Chile, who have been a surprise package at this year's tournament.
"The main aim in such a tournament is to you get through the group stage," he told FIFA. "We are in a very difficult group and we were the first team at the World Cup to qualify - for me, that is unbelievable.
"Now of course we want to finish first, and that is going to be tough enough against Chile. I had expected in advance that they would be our toughest opponents because they are very impressive.
"They are incredibly passionate and extremely well organised. And they play on the attack.
"I think they have a fantastic coach, who has persuaded his players to play football. They carry out his instructions in a passionate and persuasive way and it is beautiful to see.
"If I were allowed to choose, I'd rather not play against Brazil, although Croatia or Mexico aren't bad opponents either. But I think at a World Cup the host country always has an advantage."
Van Gaal has also hinted at rotating his squad for Monday's match, telling reporters on Sunday: "Not everyone is fit, there will be some changes take place."
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