"Given his tenure in his role, his departure was well-anticipated, and part of the natural cycle of the business," a Citigroup spokesman told Reuters. "We have a strong, talented bench that continues to support this core business."

Feig had been with the bank since 1989. His spokesperson declined to comment.

The bank had already announced the departure of another global head of its FX business, Anil Prasad, in February.

There was no indication Feig's departure was related to the global investigation into alleged manipulation of the fixing benchmarks.

According to Euromoney magazine's last poll, Citigroup sees almost 16 percent of the estimated $5.3 trillion (3.12 trillion pounds) a day that passes across the world's largest financial market.

Spot currency trading volumes in general have fallen sharply this year, however, cooled by falling market volatility in an era of universally low interest rates and, some say, the impact of the "fixing" investigation on traders.

As the investigation has intensified globally since being formally launched by U.S. and UK authorities in October last year, around 40 FX traders at many of the world's biggest banks have been suspended or fired - including some at Citigroup.

In most cases it is unclear whether the suspensions or departures are linked to the investigation.

(Editing by Jeremy Gaunt)

By Patrick Graham