The 21-year old Danish ace continues to be linked with a summer shift to Anfield and if the transfer does arise, he will go with de Boer's blessing.
"It is up to Christian what he wants," the Dutchman told reporters.
"If he feels good going to Liverpool, then it is up to him. I would want nothing more than having him with us for a few more years.
"But we realise the interest in this kind of player is huge. And I can also understand that he wants to make another step in his career. I can't stop him."