Citigroup may have to write off $15 billion in its next two quarters, a leading Wall Street analyst warned investors today, far more than the stricken bank has so far predicted.

Goldman Sachs downgraded shares in Citigroup to “sell” from “neutral”, arguing that the bank is set to suffer as the US economy slows. The stock was down more than 3 per cent in morning deals and has slumped about 40 per cent so far this year.

Citigroup shares traded down $1.69, or 4.97%, to $32.31.

On November 4, Citigroup said that it expected to write down between $8 billion and $11 billion this quarter because of its exposure to subprime mortgages through collateralised debt obligations (CDOs).

Charles Prince, the Citigroup chief executive, resigned on the same day.

Today, William Tanona, the Goldman Sachs analyst, wrote in a research note: “With deteriorating consumer and housing metrics, Citigroup is facing mounting pressure across many businesses.”

“The lack of leadership at this point in Citigroup's storied history could not have come at a worse time.”

Mr Tanona also voiced Wall Street’s mounting concern that Citi’s problems could spill over from its subprime exposure into credit cards and retail banking.

He also raised the possibility of the banking giant being forced to trim its dividend to shore up its balance sheet. The bank has already mooted the possibility of slashing dividends, divesting assets or raising new capital.

Mr Tanona also lowered his price targets for Bear Stearns, E+Trade Financial, JPMorgan Chase, Lehman Brothers Holdings, Merrill Lynch and Morgan Stanley.

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