Newcastle have told potential investors they must give a clear indication they want to make a bid for the club by Tuesday, BBC Sport understands.
Businessmen from America, the Far and Middle East make up a group of seven different potential buyers.
BBC Sport understands the takeover could be completed by the middle of November should serious buyers emerge on 7 October.
Owner Mike Ashley is believed to want about Ј250m to Ј300m for the club.
BBC Sport's Garry Richardson said on Radio 5 Live's Sportsweek South Africans make Newcastle bid ...
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"Interested parties who wish to buy Newcastle have been asked to make their intention clear by Tuesday as to whether they intend to make a serious bid for the club.
"If there are serious buyers who emerge by Tuesday, the sale could then be completed by the middle of November."
Ashley put the club up for sale in the wake of the sudden departure of former manager Kevin Keegan, but has insisted he will hold out for the right price.
A four-page 'teaser' document has been handed to interested parties, who have been asked to sign a confidentiality clause, outlining what is involved in buying the club.
On Friday, three South African businessmen liked with a possible Ј300m takeover denied they had any intention to buy the club, with billionaire Johann Rupert saying he had "absolutely no interest and no knowledge".
The South African group were considered to be the frontrunners - with their interest in bringing Keegan back making them popular with the fans.
A Nigerian consortium was also believed to have presented its bid of about Ј350m to the club, but Richardson added: "I have been told that there is no interest from Nigeria or South Africa".
(BBC)
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