Financier Amanda Staveley is ready to go through Newcastle United's books after signing a non-disclosure agreement.
Staveley – whose PCP Capital Partners firm controls £28billion of funds – is interested in buying the club, which was formally put up for sale by owner Mike Ashley early this week.
Andrew Henderson, Ashley's lawyer, has been sifting through new expressions of interest over the past few days.
Several have been described as "credible" by Henderson.
“Since Monday, a number of additional parties have come forward which we believe to be credible,” said Henderson.
“We are continuing to engage with a number of parties with whom we were engaged in negotiations prior to Monday’s announcement.”
Staveley watched Newcastle's last home game, the 2-2 draw against Liverpool early this month.
The 44-year-old is known to United manager Rafa Benitez and his associates, having led a takeover attempt at Liverpool during the 57-year-old's tenure at Anfield.
Staveley met Lee Charnley, Newcastle's managing director, as well as Justin Barnes and Keith Bishop, associates of Ashley, after the Liverpool game.
She has since had a number of meetings with the club's hierarchy. The Times has described these meetings as "productive".
Staveley, said to value United at around £300million, will now go through the books.
Ashley values the club, which he bought a decade ago for £134million, at closer to £400million, though he doesn't have a fixed asking price in mind and he is willing to "defer substantial payments" from a buyer.
None of the interested parties is understood to have yet made a formal bid for Newcastle.