Nasdaq OMX (NDAQ) chief Bob Greifeld has a pulled a disappearing act, canceling a speech scheduled for tomorrow, one scheduled for next week and fueling speculation that either hes leaving the Nasdaq or putting the finishing touches on a new deal, FOX Business has learned.

Greifelds disappearing act comes weeks after Nasdaq failed in its attempt to mount a hostile takeover of NYSE Euronext's (NYX) New York Stock Exchange, a move which, if successful, would have broken up the NYSEs planned merger with the Deutsche Borse, and after questions were raised about his handling of the effort.

In mid-May, the takeover was blocked after the Justice Department raised antitrust concerns about a possible Nasdaq/NYSE hookup, but even before the DOJs ruling, Greifeld was telling investors that he believed the deal was likely to pass muster with antitrust regulators. Those statements angered DOJ officials and prompted the Securities and Exchange Commission to force Nasdaq to issue a statement clarifying the matter.

Since that time, Greifeld has kept a low profile -- which got even lower this week as he cancelled appearances at two significant industry events: A planned speech scheduled for tomorrow at an investor conference sponsored by Sandler ONeill & Partners, and another speech appearance next week sponsored by the Tabb Group. According to the Tabb conferences agenda, Greifeld was scheduled to be its keynote speaker, and introduced by television talk show host Charlie Rose.

Sources say Greifeld is out of the country and cant be reached for the next 48 hours. A Nasdaq spokesman attributed the cancellations to scheduling conflicts, and declined further comment.

Greifelds no-shows are fueling speculation on Wall Street about Nasdaqs future -- and his own. Often, top executives cancel speaking events when they are in the middle of merger discussions and must refrain from making potentially market-moving comments. Likewise, senior corporate executives will cancel speaking events if their job is in jeopardy.

As first reported by FOX Business, Greifeld has expressed interest in buying the London Clearing House, but the Nasdaqs weakened competitive position following the failed NYSE bid might force it to merge with a bigger player, analysts and bankers say.

Greifelds contract with Nasdaq is scheduled to expire in December, according to people inside the exchange. Directly after the failed NYSE attempt, people inside Nasdaq said the exchanges board still supported Greifeld as CEO, though that sentiment may have changed as directors come to grips with the Nasdaqs difficult competitive position now that the NYSE/Deutsche Borse deal looks as if it will be successful.

Shares of Nasdaq have fallen significantly lower since its failed bid, dropping to about $24 from close to $28.

Charles Gasparino joined FOX Business Network (FBN) in February 2010 as Senior Correspondent.