Steve Bruce has echoed Newcastle owner Mike Ashley's stance that Sean Longstaff is not for sale this summer.
Manchester United have shown interest in the 21-year-old, with Newcastle demanding at least as much as Aaron Wan-Bissaka, who joined from Crystal Palace in a deal worth £50m.
Longstaff is currently out with a knee injury, causing him to miss some of the Magpies' pre-season.
Bruce, who is looking to add to his side with the signing of Stanley N'Soki, is keen to keep hold of his key assets this window.
"You never want to lose your best young players, and I think we've made it pretty evident that we won't," Bruce said.
"We're concentrating on Sean now, getting his knee right. It's his 10th or 11th training session since he hurt his knee.