The National Economic Council has in the past been a popular perch for financial heavyweights. Including Cohn, two former Goldman Sachs Group Inc veterans have served as its director. But Trump's protectionist policies and unpredictable approach to policymaking have made a once prestigious gig unpalatable for many.

“Wall Street just lost its security blanket," said Chris Krueger, policy analyst with Cowen Washington Research Group.

"We can think of no one who can fill this seat that will give Wall Street as much comfort as Cohn - particularly with the protectionists on the rise and tariffs top of the agenda."

Cohn said he would resign shortly after he lost a fight over Trump's plans for hefty steel and aluminium import tariffs.

On Bloomberg TV on Thursday, JPMorgan Chase & Co (>> JP Morgan Chase & Company) Chief Executive Jamie Dimon called Cohn’s departure from the White House “terrible.”

That sentiment was echoed at the Absolute Return Symposium, a hedge fund conference in New York, where investors fretted about the loss of Cohn as a modifying influence on Trump's rhetoric and a bulwark against economic nationalism.

“These days the markets trade hundreds of points each way based on what the president tweets and I am surprised that the markets have been as benign as they have been in the wake of this news,” said one investor, who declined to be named.

“Gary’s shoes are going to be large to fill and I have no idea who would want to take on that role."

Worries about a potential trade war after Cohn said he was resigning on Tuesday initially sent the S&P 500 down nearly 1 percent but the three major U.S. stock indexes closed higher on Thursday after Trump appeared to soften his stance on tariffs.

Trump said in a tweet on Tuesday night that he "will be making a decision soon" on replacing Cohn, the latest in a string of high-level departures from the White House.

Administration officials have said Peter Navarro, director of the White House National Trade Council, and conservative commentator Larry Kudlow were the "top two candidates" for the job. Navarro later said he was not on Trump's shortlist.

With no name from Wall Street floating among the likely contenders, a more protectionist slant in the White House is predicted in Cohn's wake.

"He brought a voice of rationality to the White House and was a strong advocate for globalisation," said Bill George, a board member of Goldman Sachs, adding that Wall Street was concerned not just about steel tariffs but also a move away from open markets.

"That’s a concern I share."

(Additional reporting by Greg Roumeliotis in New York and Pete Schroeder and Michelle Price in Washington; Writing by Carmel Crimmins; Editing by Lisa Shumaker)

By Svea Herbst-Bayliss and Catherine Ngai

Stocks treated in this article : Goldman Sachs Group, JP Morgan Chase & Company