Reuters reports that the debt-free club said it would not support a bid that involved taking on a large amount of debt to finance a takeover. It said it still had not had a definite offer from Glazer, but had held talks regarding the potential structure of any deal.
"The board has decided to inform all shareholders that it would regard an offer which it believes to be overly leveraged as not being in the best interests of the company," the firm said in a statement.
Shares in Manchester United were down 3.4 per cent at 274p in morning trading.
Glazer – owner of American football team Tampa Bay Buccaneers - has built his stake in the club to 28.11 per cent in recent weeks, fuelling speculation for a bid which could reach £787million.
Fans of the 126-year-old club have been hostile to Glazer because of reports he planned to put the team into debt to finance his takeover. This would mean spending the club's profits on paying interest on the loan, rather than players.
Manchester United said it intended to have further talks with the Glazer family and other interested shareholders.
"As a duty to shareholders, the door is always open if Glazer wants to sit down and discuss anything," a source close to the company told Reuters.
