A UK vote in favour of leaving the European Union could prompt Morgan Stanley to move its European headquarters to Dublin or Frankfurt from London, the bank's President Colm Kelleher has said.
Mr Kelleher made his comments in an interview on Bloomberg television today.
"This will be the most consequential thing postwar that we've ever seen," Mr Kelleher stated.
"Initially, the fallout can be controlled, but the political ramifications are actually quite profound," he added.
The latest polls show the outcome on the Brexit vote tomorrow is too close to call, though betting shops yesterday put the probability of a vote to leave the EU at about 26%.
The uncertainty comes as investors are grappling with continued signs that global growth remains tepid.
"We're hoping that the British voter will show sense and listen to the economic arguments and stay," Kelleher said.
"But we clearly are looking at our plans," he said, adding that the New York-based firm would consider moving its European headquarters from London.
Colm Kelleher has run the the firm's investment bank and trading division since 2013 and gained oversight of the brokerage in January, when he was promoted to president.
He has worked at Morgan Stanley or predecessor firms for more than 25 years, Bloomberg said.
A Brexit would cost a material number of UK finance positions as things like the clearing of the euro
currency would shift to the continent, he said.
Over the longer term, there would also be issues related to visas and the movement of labour.
"London cannot not suffer in the event of a Brexit vote, and the reason for that is historic," Kelleher said.
"London has done very well by virtue of being part of the European Union. Its market, the exchanges, clearing, everything is based on London", he added.
Even if the UK opts to remain in the European Union, markets are unlikely to climb significantly or return to higher trading volumes because of prolonged low interest rates and growth, he said.
When asked if the US election also affected markets, Kelleher cited oil and China as reasons for investor indecision.
"What we have seen generally is a big falloff in client volumes, and you're seeing that because of a lot of
uncertainties," he said.
"It's a number of things causing people to be very nervous at the moment. And we have seen a falloff, a significant falloff, and some could argue even a secular change because of the changes," he added.
