Netherlands coach Bert van Marwijk believes his side could be eliminated by Slovakia in the last 16 of World Cup 2010 if they take their opponents lightly.
The Oranje topped Group E with victories in each of their three games, which included a 2-0 triumph over Denmark, a 1-0 win against Japan and a 2-1 victory over Cameroon.
However, Van Marwijk was less than pleased with his team's output at times in the game against the African side and has stated a similar spell against Slovakia could cost them dearly.
"This is an opponent [Slovakia] we must not underestimate. We cannot be nonchalant," Van Marwijk told Sky Sports.
"That period of negligence [against Cameroon] we had, we cannot afford that again. It's a bit of a lesson for the next match."
Van Marwijk's side face-off against Slovakia for a place in the quarter-finals on Monday, although the Slovaks will be no easy opponents.
Despite drawing with New Zealand and losing to Paraguay in Group F, they gained qualification with surprise 3-2 victory over reigning World Champions Italy.
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