The Dutchman's side will have to remain in South America until the end of the tournament on July 13 should they progress to the semi-finals.
They will take on Costa Rica in a quarter-final clash on Saturday after securing a late 2-1 victory over Mexico in Fortaleza on Sunday.
United, who appointed Van Gaal as David Moyes's replacement in May, have scheduled a pre-season tour to the United States, which gets underway on July 17.
However, Van Gaal has told club officials that he will go straight into his new job with the former Premier League champions once his campaign with the Netherlands at the World Cup is over, according to ESPN.
The 62-year-old's first game in charge of United will be against Los Angeles Galaxy at the Pasadena Rose Bowl on July 23.