David Trainer left the company in October 2000 to set up his own research company and received a $168,000 severance package from the financial institution.
Credit Suisse claims that he broke the terms of the deal by using its own research model for his new private equity firm, Trainer and New Constructs.
The case centres around the Valuesearch product, which gives clients who use it an advantage over their competitors by focusing only on the most reliable market data.
Earlier this week, Credit Suisse agreed to pay a $536 million settlement in relation to allegations that the company illegally helped clients in countries under US sanctions to carry out financial transactions with American companies.
Prosecutors told Reuters that the company had been involved in the practice for decades, helping companies from Iran, Libya and Sudan.
By Gary Cooper