The New York Stock Exchange (NYSE) is reported to be considering whether to launch a bid for the London Stock Exchange (LSE).
NYSE could become the fourth major exchange to target the LSE
According to several Sunday newspapers, NYSE chief John Thain is currently consulting advisers about tabling a counter-bid for the exchange.
It comes days after the LSE rebuffed a £2.43bn ($4.2bn) bid from Nasdaq.
Nasdaq said it would prefer to reach an agreed deal, but has not ruled out raising its bid or going hostile.
The LSE turned down the all cash offer of 950 pence per share on Friday saying it "substantially" undervalued the firm.
Speculation now suggests Nasdaq could raise its bid to £10 per share.
However, the group could face an uphill struggle should the NYSE decide to throw its hat into the ring.
According to the Sunday Times and The Business the exchange has instructed its banker Citigroup to examine a possible counterbid.
Experts suggest the NYSE - the world's biggest stock exchange - would not like to miss the opportunity to buy the LSE - nor would it like to see its smaller rival Nasdaq steal that chance away.
However, any offer from the NYSE is likely to take at least six weeks.
The New York exchange has just made its debut on the stock market, while its merger with electronic trading network Archipelago was completed only four days ago.
But if the NYSE does decide to make an approach it will become the fourth major world exchange to show an interest in the London exchange.
Germany's Deutsche Boerse kicked off the takeover race for the exchange with a £1.25bn approach in 2004. It later walked away in the face of shareholder protests.
Since then, Paris-based Euronext has expressed and interest while Australia's Macquarie Bank recently dropped its £2.6bn offer.
An offer from a US group is expected to lead to considerable cost savings and synergies.
It would also be free of the hurdles as Euronext and Deutsche Boerse faced.
Last year, UK regulators said they would back a takeover by either firm on condition that each company ensured the independence of the London exchange's clearing provider, Clearnet.