The battle for BAA has intensified with Commonwealth Bank of Australia joining a Goldman Sachs-led group interested in buying the UK airports operator.
BAA says offers have undervalued the firm
The news comes as Spanish firm Ferrovial faces a deadline of midnight on Monday to make a final takeover offer for BAA.
Last week, BAA rejected Ferrovial's 900-pence-a-share bid for the firm.
Goldman Sachs, whose previous informal offer was rejected, has to confirm it will make a bid by 9 June or withdraw.
On Monday, BAA issued a statement saying it was is in talks with Ferrovial and "another party".
However, it added that there could be "no certainty whether any offer or revised offer will be made" as a result.
Ferrovial has until midnight on Minday to make a final offer for the airports operator.
BAA, which owns Heathrow, Gatwick, Stansted, Edinburgh and Glasgow airports, rejected a preliminary 870-pence-a-share bid from the Goldman Sachs-led group in May.
Colonial First State Global Asset management, which is owned by Commonwealth Bank of Australia, said it had been in talks with Goldman Sachs over the past few months.
Colonial First State Global Asset management has investments in Brisbane, Perth and Adelaide airports.
Commonwealth Bank of Australia said the unit would have an interest of more than 1bn Australian dollars ($752m) in the Goldman Sachs consortium if it made a successful offer.
Reports at the weekend suggested the Goldman-led group was preparing to make a £10bn bid for BAA.
If the Goldman Sachs-led consortium chooses not to make a firm bid it will be banned from doing so for a further six months under stock market rules.
BAA has said that bidders will have to pay a substantial premium above its current market value to gain control of the company because of its unique portfolio of assets.
The firm, which controls more than 90% of passenger traffic in and out of London, has said any offer should be at least 940 pence a share.