Coupled with the crisis in the financial markets this month, the French bank said that earnings would be down on last year's figures.
A large position had been built up at the end of last month and was centered on certain credit market indices, the position was built by the proprietary trading desk.
The proprietary desks use the bank's balance sheet to take bets on stocks, bonds and indices, and are becoming more popular.
But the trade was executed above the authorised limit and without authority from the bank.
Speaking to the Times, Clyon said: "The relevant disciplinary measures have been taken vis-Ã -vis the individuals concerned. The trading limit alert and security controls were immediately strengthened in order to prevent any such incident happening in the future."
The bank said that in the context of a more turbulent trading environment in September Calyon's third-quarter net result is likely to be low.