The Reds have been linked with a £22m double bid for the Danish international and his teammate Toby Alderweireld.
"It is up to Christian what he wants," Sky Sports News quotes De Boer as saying. "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.
"I can also understand that he wants to make another step in his career. I can't stop him."
The attacking midfielder, who has one year left on his contract, scored nine goals in 14 appearances in the Eredivisie last season.