Citigroup said its private bank is to set up a booking centre in Luxembourg to ensure it can continue to serve European Union clients after Britain leaves the bloc in 2019.
Citi currently operates its European private banking operations out of London.
But UK finance firms may lose their ability to sell their services to EU clients unless the British government manages to strike a deal with the bloc.
"The decision is based on what is best for our clients and what will allow us to continue to service our clients without any disruption," a spokeswoman for Citi said in a statement today.
The US bank has already said it will headquarter its EU trading operations in Frankfurt after Brexit, and has also applied for a licence for its markets business in France.
Meanwhile, Citigroup's quarterly profit and revenue beat Wall Street expectations as the bank kept a tight lid on costs, booked a gain from an asset sale and saw strength in equity underwriting.
The bank's trading revenue, despite falling 11%, was better than the 15% decline Chief Financial Officer John Gerspach forecast three weeks ago.
Trading revenue has cast a dark cloud over bank results. Rival JPMorgan Chase & Co said its trading revenue fell 21%.
Wall Street banks have seen major declines in market trading activity, which was boosted last year on global macroeconomic uncertainty, especially around Brexit and the US presidential election.
The fourth-biggest US bank by assets said today that total revenue rose about 2% to $18.17 billion, topping expectations of $17.90 billion. But revenue from fixed-income trading fell 16% to $2.88 billion.
There were bright spots as the bank's much smaller equities trading business saw a 16% increase in revenue and investment banking, which includes equity underwriting, rose 14%.
Net income rose 7.6% to $4.13 billion in the third quarter ended September 30. Earnings per share rose about 15% to $1.42 and trumped analysts' average estimate of $1.32, according to Thomson Reuters.
Expenses at the bank were $10.17 billion, 2% lower than last year.
Since taking over five years ago, chief executive Michael Corbat has been trying to boost shareholder value by cutting expenses, consolidation and buying back stock.
Consumer credit is a cause for concern for the bank as Citigroup said its company-wide net credit losses rose 17% from a year earlier. It added $194m to its loan loss reserves.
Total credit costs rose 15% to $2 billion.
Citigroup's tangible book value per share, an accounting measure of net worth, was $68.55 at the end of September, up 6% from a year earlier.
Bank of America and Wells Fargo & Co, the second and third-biggest US banks by assets, are scheduled to report quarterly results tomorrow.