The Nasdaq stock market has signalled that it may work with investment banks planning a rival trading platform if its London Stock Exchange bid fails.
Nasdaq's boss believes the LSE's shares will come down over time
Nasdaq boss Bob Greifeld said the US exchange had held talks with the group, which plans to launch a pan-European equity trading platform this year.
Nasdaq has mounted a hostile bid for the LSE, valuing it at £2.7bn ($5.3bn).
However, the London exchange has consistently rebuffed the offer, dubbing it "wholly inadequate".
Nasdaq last week said it would extended the closing date for LSE shareholders to accept its 1,243 pence-per-share offer to 10 February, amid signs of a weak response to the bid from investors.
Mr Greifeld told the Financial Times newspaper that the Nasdaq could hold on to its 28.75% stake in the LSE for 18 months if its current bid were to fail, before reassessing the situation.
He added that the US exchange would, if rebuffed, consider offering its technology to the planned pan-European trading platform, known as Project Turquoise, in a move he suggested would drive down the LSE's share price.
"In 18 months' time, we will know what is the fair value of the (LSE)," Mr Greifeld told the FT.
The LSE last month strengthened its defence against Nasdaq's hostile bid, forecasting a 180% rise in trades by 2008 and increasing its share buyback plans by £250m.
Separately, Mr Greifeld told the Daily Telegraph that Nasdaq officials had held talks with members of Project Turquoise, which include financial heavyweights such as Citigroup, Goldman Sachs, Merrill Lynch and Deutsche Bank.
"My senior people had a meeting with them last week," he told the paper's website.
Nasdaq said the likely creation of rival trading platforms, brought about by new European Union regulations, would add downward pressure to the LSE's current share price.
"It's a monopoly business today. It won't be a monopoly business tomorrow," he told the FT