Goldman Sachs analysts downgraded Citigroup shares on Monday to 'sell' citing potential write-downs of up to $15 billion in the coming two quarters, sending shares down more than 5 percent.

According to the report, Citigroup's (NYSE:C) earnings in 2009 could be damaged by mortgage-related exposure and a reluctance to take on risk in the wake of a search to replace retired chief executive Charles Prince, who left his post at the company earlier this month after heavy losses this year.

With deteriorating consumer and housing metrics, Citigroup is facing mounting pressure across many businesses, William Tanona, chief equity strategist at Goldman Sachs wrote. The lack of leadership at this point in Citigroup's storied history could not have come at a worse time.

Citigroup will write-down $11 billion in the current fourth quarter and $4 billion in the first quarter of 2008 on $43 billion in exposure securities know as collateralized debt obligations, the report said. The bank's retail and credit card businesses will be hurt by the downturn in the credit market, the analysts said.

Citigroup shares closed down $1.98, or 5.83 percent to $32.02.