David Moyes has suggested Jordan Pickford could be worth as much as £30million, with the Sunderland manager rejecting "derisory" valuations of the highly rated goalkeeper.
Pickford has been one of the few bright sparks in a dire campaign, with Sunderland relegated to the Championship after 10 years in the Premier League.
The 23-year-old has been linked with a raft of clubs, including Liverpool and Everton, although Arsene Wenger ruled out a bid to bring him to Arsenal.
Pickford was called up to the senior England squad for the first time in October and Moyes indicated Sunderland will be looking for a substantial fee for their prize asset.
"It would need to be a really, really big offer," said Moyes.
"I have said all through the season that sometimes on your journey, you may have to sell to improve.
"But I have heard some really derisory sort of figures getting mentioned and it wouldn't be any of those figures, I can tell you that."
MOYES: "Didier Ndong is under contract and he's improved. He's younger than @JPickford1 and he's had a good first season."— Sunderland AFC (@SunderlandAFC) May 19, 2017
Only one goalkeeper has ever moved for a fee in excess of £20million, with Gianluigi Buffon's £33million transfer from Parma to Juventus making him the world's most expensive stopper.
But, asked by reporters if Pickford's fee could rise as high as £30million, Moyes said: "Yes. He has been our highlight.
"For a young boy to break in and perform like that. The other night he was fantastic against Arsenal.
"Nearly everything was perfect and we will need him again this weekend at Chelsea."
|Dhawan, Rahul lead India revival in Kolkata|
|Silva not surprised by Chelsea, Spurs interest in Richarlison|
|Ancelotti, Conte, Allegri on shortlist to replace Ventura|
|Bencic doubles up with Taipei title|
|Perth Glory 0 Melbourne Victory 2: Visitors claim first A-League win of season|
|Bayliss calls for A-team matches on Ashes tours|
|Smith will bowl in the Ashes, says Lehmann|
|Marcelo unaware of Ramos-Ronaldo rift at Real Madrid|
|England book Tonga semi with PNG win|
|Celtics win 15th straight, 76ers in collapse against Warriors|
|Lehmann tells Australia: Get behind the Ashes team|
|Goffin revels in career-best win after upstaging Federer|
|Neymar will take PSG´s next penalty - Cavani|
|Ranieri would consider coaching Italy|
|It´s been an amazing year - Federer signs off for 2017 after London exit|
|Postecoglou set for decision on Socceroos future|
|Celtics coach Stevens wants more despite 14-game streak|
|Kerr: What Embiid did against the Lakers was terrifying|
|Cook extends lead at RSM Classic|
|Frampton beats Garcia by unanimous decision in front of Canelo|
|Championship Review: Millwall deny sloppy Sunderland, Wolves back on top|
|Simeone rallies around under-fire Griezmann|
|Hogg and Barclay ´gutted´ to let All Blacks escape|
|It´s a growth process - Montella optimistic despite Napoli loss|
|Spalletti happy at Inter, tips Ancelotti for Italy job|
|Sarri defends sacked Ventura over Insigne´s Italy snub|
|Los Blank-os! Misfiring Real Madrid break new ground under Zidane|
|Zidane upbeat despite derby stalemate|
|Zidane unsure on Ramos absence with suspected broken nose|
|Mind the gap! Real Madrid must make history to retain LaLiga title|
|Dimitrov denies Sock to book Goffin showdown|
|Springboks gain measure of revenge over 2023 RWC hosts France|
|Alonso fuels Le Mans talk with WEC rookie test|
|Napoli 2 AC Milan 1: Insigne stars after Italy snub as leaders move four points clear|
|Atletico Madrid 0 Real Madrid 0: Defences dominate in historic derby|
|Wasps sting Falcons, Warriors off the mark|
|Montpellier take charge of Top 14 as Lyon slip up|
|Pjaca scores winner for Juventus Primavera on return from injury|
|Jones bristles at suggestion England ´got lucky´|
|Lions don´t recover like humans! - Ibrahimovic and Pogba thrilled to be back|
|Pogba was different class - Mourinho praises midfielder after impressive comeback|
|Competition is good – PSG boss Emery explains benching Mbappe|
|Klopp apologises after Moreno misses birth of child|
|Experimental Ireland XV survives Fiji scare|
|Cheika makes no excuses after controversial calls hurt Australia|
|Valiant Scotland fall short against clinical All Blacks|
|Manchester United 4 Newcastle United 1: Pogba shines as Ibrahimovic makes his return|
|Hodgson accuses Niasse of diving to win Everton penalty|
|´Why not?´ - Hazard believes Chelsea can catch City|
|Roma 2 Lazio 1: Nainggolan stunner proves decisive|
|Bournemouth hat-trick hero Wilson: I need to be selfish|
|Valverde admits scoreline in Leganes win was ´excessive´|
|Pulis leaves uncertain future to West Brom board|
|Results not far away for struggling Swansea, claims Clement|
|Heynckes proud of 500 Bundesliga wins as Bayern go six points clear|
|Al-Hilal 1 Urawa Red Diamonds 1: Rafael earns valuable first-leg draw|
|Stones could be set for six-week spell on sidelines|
|Paris Saint-Germain 4 Nantes 1: Cavani double puts hosts six clear|
|Guardiola delighted to maintain rhythm after international break|
|Woeful Sunderland set new record ahead of expected Coleman appointment|
|Suarez unmoved despite ending Barca drought|
|Cheika fumes as England claim controversial win over Wallabies|
|Thumb injury ends Coleman´s tour|
|Leganes 0 Barcelona 3: Scruffy Suarez double ends goal drought|
|Amos try the difference as Wales labour to Georgia win|
|Crystal Palace 2 Everton 2: Niasse equaliser boosts Unsworth´s case|
|Heynckes reaches record 500th Bundesliga win|
|Bournemouth 4 Huddersfield Town 0: Hat-trick hero Wilson stars for 10-man Cherries|
|Burnley 2 Swansea City 0: Old boy Cork stars as Dyche´s men win again|
|Liverpool 3 Southampton 0: Record-breaking Salah blows Saints away|