MORGAN STANLEY: We will 'certainly' move people out of London before Brexit happens
"It is the cost of doing business," Kelleher said when asked about applying for European licenses now.
"We can't wait two years to decide what we're going to have to do, and we will have certainly to move some people well before that two years is up in order get ready and to be prepared for what will happen."
He was speaking at Morgan Stanley's European Financial Services Conference.
British Prime Minister Theresa May will trigger EU divorce proceedings on March 29, launching two years of negotiations that will shape the future of Britain and Europe.
"Of course what's happening is we have various cities - Paris, Frankfurt, Dublin, and others - talking to us, and the rules are changing there as well," Kelleher said.
"They are changing the dynamic of where we will be and what we will be and what we will do."
He also said you may see some business moving to New York.
Kelleher said Morgan Stanley is trying to be as prudent and careful as can be in monitoring the Brexit negotiations, emphasizing that whatever the firm ends up doing will affect employees who have "children and so on" - so "you can't just order them around like units on a board."
Ultimately, he said, Brexit is a "distraction."
"I would much rather it hadn't happened, clearly," he said.