Societe Generale has filed a legal complaint against the trader accused of defrauding the bank which led to a loss of 4.9bn euros ($7.1bn; Ј3.7bn).
While Societe Generale has yet to name the trader, media reports say he is 31-year-old Frenchman Jerome Kerviel.
SocGen's chairman Daniel Bouton called the fraud a "one-off" and denied it was a trading or risk-management fault.
But analysts say Mr Bouton's future looks uncertain after the bank's failure to detect the malpractice.
They also say that the losses have left the bank vulnerable to a takeover bid.
(BBC)
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