De Jong spent the majority of the summer linked with a transfer to Manchester United, but a move away from Barcelona never materialised.
Despite remaining at Camp Nou, Erik ten Hag could still make an attempt to sign the player that he once managed at Ajax when the transfer window opens in January.
However, the United boss may be concerned by Van Gaal’s comments after a hamstring issue forced De Jong off at half time in Netherlands’ 2-0 win over Poland on Thursday.
Commenting on De Jong’s fitness, Van Gaal said: “I have let go of that dogma [only selecting players that play for their club] for a long time, otherwise I would not have selected Steven Bergwijn, for example.
“Memphis [Depay] and De Jong are two very important players who have left. I have encouraged them: I will keep a place for you for as long as possible, but you have to be fit.
“The fact that the Dutch national team is not a rehabilitation centre certainly applies to the World Cup, but I have to trust that they are fit when they say that.
“They have meant so much to this Dutch team, I have to reserve a place for that. Because we are 26, I can easily select players.
“In 2014 I did the same with [Georginio] Wijnaldum. One has earned more pluses than the other. Memphis has scored goals and provided assists and has been so important, just like De Jong.
“His qualities to be able to cope with the pressure of the opponent. We are not the only ones who put pressure on the ball, several countries do that.
“Frenkie de Jong is a determining factor. That’s why I look at being complementary to De Jong, but I also see if I can find someone else for it because we have to be prepared. You never know how a hamstring injury will turn out.”
Despite De Jong’s absence, the Netherlands clinched a place in the UEFA Nations League semi-finals after a Virgil van Dijk goal guided them to a 1-0 victory over Belgium.
Van Gaal will now turn his attention to the World Cup, with the Netherlands drawn in Group A alongside Qatar, Ecuador and Senegal.