But in a statement on Monday it said it would not hold any more talks unless a definitive offer was put on the table.
"The board of Manchester United confirms that at a shareholder meeting Glazer has indicated, on a very preliminary basis, potential revisions to its previous proposal," the 15 times champions said in a statement.
"The board does not intend to open discussions on this matter unless it receives a definitive proposal from Glazer," United added.
The Takeover Panel has put the club into an offer period and can to issue a "put up or shut up" statement to force a firm offer within a set period.
Glazer's latest attempt to win control of the club comes a month after his bankers resigned after the US tycoon used his 28 per cent stake in United to oust three of its board members during the club's annual general meeting.
