National team officials confirmed that Timber, 25, sustained a mild concussion following a collision in Thursday's practice.
Medical staff monitored the player immediately after the incident and decided he would be unavailable for selection.
"The moment Quinten had the ball, I ran deep," teammate Teun Koopmeiners told Dutch media. "He wanted to chip it to me and then it happened. It wasn't a super hard collision, as I understand it, but you do have to be careful."
The setback for Timber, who celebrated his 25th birthday on Wednesday and was a substitute in the Netherlands' opening 2-2 draw against Japan. His twin brother, Jurrien, has already been forced to miss the tournament with a groin injury.
Having joined the Dutch preparations late following Arsenal's defeat by Paris Saint-Germain in the Champions League final, the defender was forced to drop out of the squad shortly before a warm-up friendly against Uzbekistan in New York.
FIFA World Cup 2026
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