Michael Clark, global head of equity proprietary trading at Credit Suisse First Boston, is the fifth ally of John Mack, former chief executive, to leave the bank since Brady Dougan succeeded Mack in July.

Clark, who spent 14 years at the bank including stints as global head of cash equity trading and co-head of global equities, will leave at the end of February to "pursue personal interests" according to an internal memo seen by Financial News.