Steve McClaren has warned the clubs tracking Luuk de Jong they will have to make him an offer he "cannot refuse" to take the striker from FC Twente.
Highly-rated De Jong has been a long-time target of Newcastle boss Alan Pardew, although the Premier League side are facing competition from Germany with Borussia Monchengladbach said to be ready to table a bid.
But McClaren has dug his heels in with the FC Twente board over the proposed sale of the starlet as well as Brazilian defender Douglas to the Magpies.
Douglas, a powerful centre-back, is reportedly being tracked by Liverpool, Arsenal, Tottenham, Aston Villa as well as Newcastle.
The former England boss says he is not under pressure to sell the pair after balancing the books by offloading Ola John to Benfica.
McClaren told Sky Sports News: "We do not have to sell and, football being football, everybody has his price. For Luuk de Jong to leave this club then it will have to be a very good offer, one that we cannot refuse, and at the moment no-one has given us that yet.
"There are more than just rumours. There is obvious interest as everyone knows.
"Of course we want to keep Luke de Jong and we want to keep our squad of players as it is. We want to build and not to take players away.
"We have already sold Ola John and I have told the club I do not want to sell any more."
De Jong scored an impressive 25 goals for his club last season and was part of Holland's Euro 2012 squad.
But despite being the joint-second highest scorer in Holland last time out, McClaren believes he should wait another season before moving abroad.
"The timing has to be right he leaves," he continued. "I would advise Luke to spend another year establishing himself in Holland doing it again, getting 25 or 30 goals and being a top striker, another year more mature, another year closer to the national team as he is in the squad now.
"Any club taking him now would not be getting the best of him. They will be getting the best of him in a year's time - if they can afford to do that."