Ajax boss Frank de Boer has warned Louis van Gaal and Manchester United that Jasper Cillessen will now cost a 'huge' amount after they delayed making a move for the goalkeeper.
The Red Devils are currently considering their options in goal, with number one David de Gea seemingly close to joining Real Madrid.
The Spanish international was dropped for the 1-0 win against Tottenham at Old Trafford yesterday, with summer arrival Sergio Romero taking his place. De Gea is out of contract next year and won't sign an extension, however the Red Devils remain adamant that they'd rather let him walk away for nothing next year than sell him for a discounted price now.
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Real Madrid's reluctance to pay a fee in excess of £25 million has left Manchester United in limbo as they decide whether to bring in a long-term replacement - which Romero isn't viewed as - now, or wait to assess their options next summer when Hugo Lloris may be available.
That has forced up Cillessen's price, with the end of the summer transfer window approaching. The Dutch international is on Van Gaal's list of potential replacements and a price of £25 million was initially quoted by Ajax.
However that number could now be much higher according to De Boer, who also insists that Ajax will fight against selling up now with less time to find a replacement.
The former Holland international said: "Man United will have to pay huge price for Cillessen.
"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."