"He doesn't follow our philosophy. There is no place for someone like that," said the Dutchman. "The philosophy is how you play football, and how you maintain your match rhythm.
"For example, he refused last (season) to play in the second team. That's also one aspect of our philosophy but there are a lot of other aspects in the philosophy of how you have to play like a goalkeeper in Manchester United.
"When you are not willing to follow the principles of the philosophy, then there is only one way and that is out," continued van Gaal.
Asked directly if he was selling the player, the manager replied: "Yes. For us it is a big disappointment because we thought he would follow our philosophy.
"When you are not playing in the first selection, then you must play in the second selection. Every player has to do that and he refused to do that."
Van Gaal had said in February, a month after Valdes joined United on an 18-month contract from Barcelona, that the Spaniard must earn his spurs with the reserves before he could be considered for a full first-team debut.
Valdes, who was a surprise omission from United's squad for the tour, failed to displace incumbent David de Gea, who has been linked with a move to Real Madrid and whose contract expires at the end of next season.
(Reporting by Alan Baldwin, editing by Nick Mulvenney)
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