Ajax boss Frank de Boer has warned Manchester United that the asking price for keeper Jasper Cillessen is going up by the week, according to the Daily Mirror website.
United are plotting a £25million swoop for Cillessen if their Spanish No 1 David De Gea gets his wish to join Real Madrid.
However, De Boer 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.”