Deutsche Boerse declined to comment when asked on Tuesday whether the group was interested in U.S. Nasdaq Stock Market Inc's stake in London Stock Exchange.
I cannot comment, Chief Executive Reto Francioni said in response to a question after delivering a speech at a banking conference.
Nasdaq is trying to sell its 31 percent stake in the LSE to help finance a planned acquisition of Nordic stock exchange operator OMX.
Deutsche Boerse, which is completing a takeover of U.S. derivatives market International Securities Exchange (ISE), is seen by analysts as an unlikely candidate to buy the Nasdaq stake.
Financial industry sources attending the conference interpreted Francioni's reply as a strategy intended to avoid painting Deutsche Boerse into a corner.
In spring 2005, the German group's shareholders rebelled, ousting Francioni's predecessor Werner Seifert, after Deutsche Boerse had launched an unsuccessful bid for the LSE.
Some Deutsche Boerse shareholders were up in arms again this spring, opposing the $2.8 billion ISE acquisition, which Deutsche Boerse expects will close in the fourth quarter.
Why would the view of the shareholders have changed since? one source said, speaking on the sidelines of the conference.
But in an unlikely scenario where Nasdaq would offer its LSE stake at a fire-sale price, it was not inconceivable that Deutsche Boerse might reconsider -- hence Francioni's cautious reply, the source told Reuters.
The Wall Street Journal reported on Tuesday that Nasdaq has given potential suitors until the end of the week to express interest in its LSE stake.
That was not, however, a hard deadline, the newspaper said, citing two people familiar with the matter.
Deutsche Boerse's shares traded 0.7 percent higher at 81.28 euros at 1110 GMT, with LSE shares up 1.4 percent, OMX 0.6 percent higher and Nasdaq's Frankfurt-traded share up 0.2 percent.
An index of the world's leading exchanges was 0.1 percent higher.
Deutsche Boerse said after the market's close on Monday that the combined cash equities turnover in its Xetra electronic order-matching system and on the Frankfurt stock exchange floor increased 109 percent year-on-year to 266.1 billion euros ($361.5 billion).
Trading volume on Deutsche Boerse's derivatives platform Eurex increased 64 percent to 175 million contracts.
DZ Bank analyst Matthias Duerr said volumes in the first two months of the third quarter suggested revenue growth ahead of his forecast for Deutsche Boerse.
Duerr said in a research note referring to the trading statistics that he saw upside potential for his full-year 2007 earnings-per-share growth forecast for Deutsche Boerse, and reiterated his buy recommendation and fair value of 90.50 euros.