A broker in London is said to be tied in with rogue trader Jerome Kerviel's £3.6bn fraud.
The man, known as Mat, is mentioned in e-mails between Kerviel and colleague Moussa Bakir.
But reports have claimed Mat never existed and Kerviel made him up to cover his tracks.
So far, French detectives have failed to find him. Kerviel lost billions in spread bets.
The 31-year-old said he worked alone but claimed bosses at Societe Generale turned a blind eye to his risk-taking, as long as he was making money.