The coach admitted he is still struggling to come to terms with the loss of one of his star players for this summer's showpiece event in Brazil
The Roma ace was cruelly ruled out of the upcoming tournament in Brazil after tearing his anterior cruciate ligament in the Italian side'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 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.