Deutsche Bank has set up a "working group" to review whether to move parts of its British divisions to Germany if the UK leaves the EU.
The working group has been established, but it is "early days and no decisions have been made", a spokesperson for the bank told the BBC.
Prime Minister David Cameron has promised a referendum on the UK's EU membership by the end of 2017.
Deutsche Bank employs 9,000 people in the UK.
It is the first of the banks to publicly state that it is formally examining the potential fallout from the referendum, according to the Financial Times, which first reported the story.
Many businesses have urged the government to bring forward the referendum to end the prolonged wait.