Rams boss Nigel Clough has warned they won't get the crown jewel of his Championship side on the cheap.
Clough said: "Nobody knows what we want or what the fee is going to be come the time, because we have not got a specific valuation in mind.
"Would it be more than £6m? Yes, I think it is fair to say that.
"We just think it is going to be a very, very substantial figure to tempt him away. We've had no bids or contact from anybody.
"If someone comes in through the front door and makes an official enquiry or bid, we will have to react to it.
"Unless there is somebody sitting there with an awful lot of money burning a hole in their pocket I cannot see it changing."
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