Manchester United have been warned they will have to spend big if they are to sign Ajax goalkeeper Jasper Cillessen, with the Dutch club's coach Frank de Boer claiming his price is rising by the week.
United keeper David de Gea appears set to join Real Madrid before the end of the summer transfer window after he was left out of their opening day victory over Tottenham on Saturday.
Cillessen - who played under Van Gaal for Holland at World Cup 2014 - has reportedly emerged as the number one choice to fill the void at Old Trafford.
But Ajax will not part ways with the 26-year-old without a fight, having missed out on replacement keepers Maarten Stekelenburg and Wojciech Szczesny, who joined Southampton and Roma, respectively, on loan.
"Man United will have to pay huge price for Cillessen," De Boer is quoted as saying in the Mirror.
"Let it be clear that we are going to take a really strong attitude and we will fight against him leaving at this stage.
"Why? Because we have seen all our three alternatives go out of sight and it gets harder and harder to find a decent replacement.
"To make it clear, Jasper is getting more expensive by the week, although there are certain figures that we can't turn down."
