Citigroup has drafted in Richard "Rick" Stuckey to help to disentangle the world's largest bank from its $43 billion (£20.6 billion) of exposure to American mortgage-related assets, drawing on the same man who helped to unravel the collapsed hedge fund Long Term Capital Management (LTCM).

Mr Stuckey takes charge of the portfolio only a day after Citigroup gave warning that as much as $11 billion had been wiped off the value of its sub-prime-related assets.

The bank said that it was facing an after-tax hit as a result of between $5 billion and $7 billion.

It comes barely a day after Charles "Chuck" Prince, the Citigroup chief executive, was forced to step down after four years at the helm amid sliding quarterly profits.

Citigroup, increasingly reeling from the credit market turmoil, said that the fair value of its exposures remained unclear and that it might have to write down "materially" more value.

According to a memo circulated at the bank yesterday, Mr Stuckey will run a "dedicated team to focus solely on managing these [sub-prime-related] assets and their resultant exposures.

The new group, to be called the Sub-Prime Portfolio Group, will draw on various experts within the bank, including Mark Tsesarsky, the current head of special situations in securitisations.

The memo read: "In the coming weeks we will review our credit businesses to better align them with the future opportunity [sic]. We are a leader in these businesses and we believe they continue to represent a great opportunity for our institution going forward, including structured products."

Mr Stuckey, a former head of risk management at Citigroup, was one of six managers brought in at LTCM in 1998 after the former high-flying hedge fund suffered losses of $4.6 billion.

He was responsible in part for helping to unwind LTCM's $90 billion of positions.

According to Bloomberg, Mr Stuckey worked at Salomon Brothers, when John Meriwether, the founder of LTCM, was a vice-chairman.

He co-ran a derivatives unit with Myron Scholes, the Nobel prize-winning options pricing guru who was a partner in LTCM.

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