The defender has endured an error-strewn season to date but his international manager says small changes at club level could make the difference
It was the latest in a series of errors the 20-year-old defender has made this term, but Koeman has backed De Ligt to come good.
“It is clear that he has to make a change in the way he plays at his club,” Koeman told reporters.
“That can sometimes be at the expense of the confidence of a player, but Matthijs gets full confidence from us, and I am sure that in the end he will only get better.”
Netherlands will be without Memphis Depay when they face Belarus on Sunday, the forward having scored twice in the comeback win over Northern Ireland in Rotterdam.
“It was too great a risk to let him play,” said Koeman of Depay, who has dropped out of the squad due to a thigh issue.
“Of course it is a shame, you always miss players like this, but luckily we have more good attackers.
“We had already made the decision to select an additional attacker. We are playing with three attackers tomorrow, and we have three behind them. That seems enough to me.”
The state of the pitch in Minsk has made headlines but Koeman is unconcerned about the Dinamo Stadion surface.
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“I took a look at it, but it didn’t even bother me that much,” he added. “It didn’t matter that much that we now train on a side field.”
The Netherlands moved to the top of Group C with that win over Northern Ireland on goal difference ahead of Germany with three qualifying games remaining.
Wins over Belarus and Estonia in their remaining fixtures should be enough to secure their place at next summer’s finals, their first major international tournament since the 2014 World Cup in Brazil.