While Deutsche Boerse has an agreement in place to acquire NYSE Euronext, other suitors haven’t given up. Nasdaq, the Intercontinental Exchange and CME (Chicago Mercantile Exchange) Group have held various talks about a combined bid for the world’s largest stock exchange, according to numerous bankers involved, reports CNBC’s David Faber.

“I'm told the CME also briefly spoke with Brazil's BM&FBovespa about a joint bid, but those talks made no progress,” he writes on CNBC.com.

The likelihood of an actual bid to circumvent the agreement already in place is quite low, Faber notes. First, joint hostile bids to supersede an existing arrangement rarely happen.

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In addition, the NYSE has grown through acquisitions including Archipelago and Euronext, each of which has a cost basis. So an acquirer may be responsible for taxes created through the sale of these units as part of the NYSE.

Then, of course, there’s the $340 million break-up fee that any purchaser of the NYSE must pay to Deutsche Boerse.

“You get no shortage of hurdles to any possible bid,” Faber says.

Some experts see the NYSE-Deutsche Boerse combination as a very strong entity.

"Clearly they would be a leader across a variety of different asset classes, including obviously European stocks," Adam Sussman, director of research at Tabb Group, a financial research firm, tells Dow Jones.

"The combination of Euronext and their various markets they run and then adding Deutsche Boerse to that would be a pretty powerful combination."