The Feyenoord midfielder is believed to be attracting interest from a number of other clubs, including Fiorentina, but his representative claims that any negotiations between the two parties will have to wait until after the World Cup.
"There has been no contact recently with the Viola or with the Red Devils and neither with other clubs," Wessel Weezenberg told Calciomercato.
"He is focused exclusively on the national team. The opportunity to train daily with a great coach like van Gaal is very important for him.
"Jordy's future will probably be decided after the World Cup."
Louis van Gaal, who will begin his duties as Manchester United manager later this summer, included Clasie in his Dutch squad for the tournament in Brazil.