Newcastle have confirmed to the Stock Exchange that majority shareholder Sir John Hall has been approached to sell his stake in the club.
Hall, who paid an estimated £3m to take charge of the club in 1991, stepped down as chairman in 1997.
Weekend newspaper reports suggested an American-backed consortium had been working on a buy-out proposal.
A club statement said an approach had been received "which may or may not lead to the disposal of the stake."
Hall represents Wynyard (Guernsey) Limited, which owns 28.8% of Newcastle United plc, while his son Douglas, who is still deputy chairman of the club, owns a further 13% stake in the club.
Club chairman Freddie Shepherd's company, Shepherd Offshore, recently increased its holding in the publically listed club to 27.29%.
Hall's era in charge of the club took in many of their recent highlights.
Having replaced Gordon McKeag in the boardroom, he appointed former Magpies player Kevin Keegan as manager, and sparked the club's resurgence.
Under Hall's guidance, Newcastle twice finished runners-up in the Premiership, played in the Champions League, and completed the then record £15m purchase of Alan Shearer before Hall stepped down in 1997.
Freddy Shepherd replaced him, since when, despite twice reaching the FA Cup final, the club has fallen off the pace in the Premiership, even though they have invested heavily in players like Michael Owen and Albert Luque.