The summon by a Singapore private banking client was rejected Friday by Citigroup (C.N). The client claimed that he has lost more than S$1 billion as the bank made available wrong information and failed to execute some of his trades.

In a court filing, Citi clarified that businessman Oei Hong Leong was presenting a considerable appetite for risk and an understanding of the risk and exposure associated with the various derivative investment structures entered into.

The bank added that his open positions with Citi had stood as high as $6.89 billion in February 2008.

With the collapse of Lehman Brothers last September that created turmoil in financial markets, many private banking clients lost money. 

City, which claimed that Oei's claims of a "meltdown" in its tracking and control systems were "contrived afterthoughts", denied of providing him with incorrect and misleading margins numbers. 

Citi's private bank said in a statement, "We intend to vigorously defend the action. We have today filed our defense."

In its defense for failure to execute $600 million worth of buy orders for U.S. Treasury bonds placed by Oei, City specified that was because Oei had consistently set his limit prices below the indicative market prices.

Citi was sued by Oei, one of Singapore's richest men, last month for negligence and misrepresentation Oei had a long relationship of 30 years with the bank.