Newcastle chairman Freddy Shepherd knew nothing of businessman Mike Ashley's takeover bid, BBC Sport understands.
Shepherd was unaware of Ashley's purchase of Hall's shares
Shepherd was in hospital with suspected pneumonia when told Ashley had bought Sir John Hall's 41.6% stake for £55m.
Ashley has now launched a £133.1m takeover bid but Shepherd told the Daily Express: "There is nothing he can do unless he gets 75% of the stake.
"He can't take full control. He must now make an offer for the shares held by all the shareholders."
I'm as shocked about this as chairman Freddy Shepherd
Newcastle manager Sam Allardyce
Ashley bought his shares through his firm St James Holdings Limited (SJHL), which he established specifically for the purpose of investing in Newcastle.
Under stock exchange rules, Mr Ashley's company now has to make a cash offer for the remaining shares - with a stake of around 29.8% belonging to Shepherd.
And Shepherd added: ""He has spent more than £50m but will have to spend a lot more.
"He can't change resolutions or the club's articles of association."
Magpies manager Sam Allardyce was also taken by surprise by Ashley's bid.
"I'm as shocked about this as chairman Freddy Shepherd," Allardyce told The Sun.
"I will be going to see the chairman to see what this all means.
"I don't know anything about the person hoping to take over but he must want good things for Newcastle if he is spending such an amount of money on the club."
Newcastle finished last season in 13th place in the Premiership and Glenn Roeder resigned as manager on 6 May after 15 months in charge.
Allardyce, who stood down as Bolton boss after eight years in charge at the Reebok Stadium on 29 April, was named as the new manager at St James' Park earlier this month.