The head of European credit sales at Credit Suisse, Nicholas Kyprios, has been fined £210,000 by the Financial Services Authority (FSA).
The fine was for disclosing confidential information about a client ahead of a bond issue in November 2009.
Mr Kyprios gave a fund manager inside information about the takeover of UnityMedia by Liberty Global, despite being told in writing not to do so.
Credit Suisse also fined Mr Kyprios, who is still working for it
The information revealed included the fact that the bond issue was linked to a takeover and that it was due to be announced the following day.
The FSA said that Mr Kyprios had played a "guessing game" with a fund manager, giving clues such as "getting warmer".
"While the FSA accepts that he did not set out to disclose the information, Kyprios' conduct in trying to push to the limit what he could say resulted in him crossing the line," said Tracey McDermott at the FSA.
"His behaviour was well below the standards we expect of senior market professionals who we should be able to rely on to uphold the system rather than seek to get round it. The high penalty reflects the seriousness of Kyprios' breach."
The fine was reduced from £300,000 because Mr Kyprios agreed to settle at an early stage.
Credit Suisse said in a statement: "We deeply regret that one of our employees was sanctioned by the UK FSA for breaches related to our information policies."
"Credit Suisse fully supports the FSA's actions to ensure information is properly controlled and has reinforced the FSA's decision by imposing its own financial penalty on the individual."
Sources at the bank said that Mr Kyprios had been fined 50% of his variable compensation for 2011 in addition to the FSA fine.