Citi warned, in a regulatory statement filed in the United States, that it is could plead guilty to Department of Justice allegations over currency market manipulation.
It said: "A resolution with the Department of Justice could include a guilty plea on an antitrust charge."
The DoJ is probing six banks, including Citi, for attempted rigging of foreign exchange rates.
In November last year, Citi was fined $359 million (£230 million) for FX fixing by the Financial Conduct Authority (FCA) in the UK and the US Commodity Futures Trading Commission (CFTC).
HSBC already paid $343 million (£220 million), JPMorgan $352 million (£226 million), the Royal Bank of Scotland $344 million (£220 million) and UBS $371 million (£238 million) to settle currency market manipulation allegations with the same regulators.
The currency market is one of the largest and most liquid markets in the world. It has a daily average turnover of over $5 trillion (£3.2 billion).
