The 24-year old Iceland international is a target for Scottish champions Celtic but Heerenveen sporting director Gaston Sporre said he will only depart if the club receives a considerable offer for his services.
"He's good for at least 20 goals a season for us and we won't sell him for a reduced fee," said Sporre.
"If we get a concrete offer for him we will negotiate, but our aim is to keep him here at Heerenveen. He hasn't told us he is unhappy or asked for a transfer. We will wait and see."