Strootman was cruelly ruled out of the upcoming World Cup in Brazil after tearing his anterior cruciate ligament in Roma's 1-0 loss to Napoli on March 9.
The 24-year-old, capped 25 times at international level, will watch from the sidelines as the Netherlands do battle with defending champions Spain, Chile and Australia in Group B.
"Strootman is a player who brings a balance to the entire team," Van Gaal told Soccernews.nl .
"I will have players like Rafael van der Vaart and (Wesley) Sneijder, of course, but no one will be able to replace Kevin.
"But anyway, as long as we are all in good form we have a good chance to get through the group stages."
The Netherlands, who face Ecuador, Ghana and Wales in the lead up to Brazil, will kick-off their World Cup campaign against Spain in Salvador on June 13.
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