The 18-year-old, who has broken into the England U21 set-up, is among the most sought-after talents outside of the Premier League.
A number of top-flight clubs would welcome the opportunity to acquire his potential, but no moves have been made as yet.
Derby are bracing themselves for a flurry of activity before the summer transfer window closes, but have made it clear that Hughes will not come cheap.
Clough told the Derby Telegraph: "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."