NYSE-Euronext suffered its first major setback last week as CEO John Thain, 52, looked poised to replace Stan O’Neal as boss of Merrill Lynch.

Wall Street was shocked at the news as Larry Fink had seemed quids in for the post. Thain was formerly President of Goldman Sachs.

The move leaves a hole at the top of stock exchange group NYSE-Euronext as the man who forged the transatlantic merger jumps ship.

Chief operating officer Duncan Niederauer looks poised to take control.

Merrill’s share jumped 5 percent as Wall Street absorbed the news.