PSV head coach Ruud van Nistelrooy is concerned about the prospect of losing Noni Madueke, amid reported interest in his services.
The 20-year-old has been touted as a potential target for Chelsea this year, as Todd Boehly continues to splash the cash in a bid to rejuvenate the squad at Stamford Bridge.
Madueke has been limited to just four Eredivisie appearances this season due to injury but is well known in England due to his Under-21 international appearances and youth spells with Crystal Palace and Tottenham.
PSV's reluctance to approve a deal comes after already offloading one of their prized assets in the mid-season transfer window, having sold Cody Gakpo to Liverpool for a €40million (£35m) fee.
Van Nistelrooy is aware of similar interest in Madueke and expressed his worry at the situation, though he was aware it would be out of his hands if a suitable price is offered.
"I know there is interest. This is due to his qualities and performance. It's worrisome," he told De Telegraaf.
"We need to see if we can keep him. I very much hope for that. We must do everything we can to do that.
"You also know that things can take off if the purse is pulled hard.
"Then you have to be ready with several options, because then you would lose the second player in the winter. But as a coach you would rather keep your best players."