I know some people need it spelled out before facts finally strike home, but are you actually aware that he is DUTCH? If Holland want him for a game in future years, Holland GET him - YES ?
What happens if NUFC have a crucial FA Cup match etc etc at the same time ?
It doesn't matter whether he's from Holland, Scotland, or Australia, his international commitments come first as far as FIFA are concerned - are you a little clearer, or do we have to write in on the blackboard ?
If a player is English the chances are that other teams will have the same calls on many of their players, esp with the moves now towards having a minimum of National players in Prem sides.
International fixtures have their own specified dates which don't clash with club games. It's not like he's gonna go to the ACN to play for Holland.