Van Gaal's United to play Valencia
Van Gaal's role as Holland coach will end after Saturday's third-place play-off against Brazil at the World Cup and he will then turn his attention to making the Red Devils competitive again after last season's seventh-placed finish - a dismal season which cost David Moyes his job.
The Valencia friendly is also likely to feature new signings Ander Herrera and Luke Shaw playing at their new home for the first time.
"This event marks the start of the next chapter at Old Trafford. With a new manager and new players making their first appearances in front of a home crowd," said group managing director Richard Arnold.