Malen impressed in the Netherlands’ 3-0 win over North Macedonia in their final group game, while Weghorst scored in their opening 3-2 win over Ukraine.
The Dutch takes on the Czech Republic in their Euro 2020 last-16 clash with plenty at stake and de Boer keen to keep his opponents guessing.
“The Czechs try to put pressure early. Then you can say that there is space and you need a fast player,” he said.
“But if you cant play out of it, you need a cue point for the long ball. So you’ll see who’s playing tomorrow; Donyell Malen or Wout Weghorst.”
On 22-year-old PSV Eindhoven forward Malen, he added: “Ruud van Nistelrooy is right that it is Malen’s international breakthrough but he will have to show it every time he plays.
“I think he has what it takes to become a major international player. If you’re a connoisseur and you like football, you can see the quality in him.
“That is why everyone is very charmed by him.”
The Czechs got through in third spot in their group but impressed with a 2-0 win over Scotland and 1-1 draw against Croatia.
“Which opponents are in form is an afterthought. We have to take care of every game,” he said.
“We are now looking at the Czech Republic. We have a big problem with that.”