"We are lucky in the sense that we have a major bank in France," group chairman Douglas Flint told BBC Radio 4's Today programme.
"So, if we were to leave and if there were to be restrictions, ultimately on the renegotiation of Britain's position, we have the ability to move activity and people between London and Paris," he said.
Commenting on the bank's decision to remain headquartered in London, Flint warned the result of the referendum "potentially does have an impact on the operating activities of our wholesale bank".
The bank's chief executive Stuart Gulliver told Sky News said a British departure from the EU could have a "significant impact" on the bank's trading room, corporate banking and investment banking.
"We have 5,000 people in global banking and markets in London and I could imagine that around 20 per cent of those would move to Paris," he said.
Any decision on moving jobs would depend on the terms of a British exit, including whether Britain could still access the financial services "passporting" regime allowing member states to trade across national borders.
Prime Minister David Cameron is headed to Paris to meet French President Francois Hollande today on a crucial week culminating in a summit in Brussels where he is hoping to renegotiate Britain's EU membership.
Opinion polls indicate a close race between supporters and opponents of Britain staying in the EU and big businesses have voiced concern about the impact from the uncertainty ahead of the vote.
