Reuters reports that the lawsuit, which is expected to be filed on Wednesday, will allege that Credit Suisse misrepresented the quality of loans packaged in securities, according to the source.
Investors lost more than $11.2bn, the source added.
The news agency also reports that The Securities and Exchange Commission cannot revive a securities fraud claim against Goldman Sachs bond trader Fabrice Tourre over the sale of complex securities linked to subprime mortgages, a federal judge ruled on Monday.
U.S. District Judge Katherine Forrest in Manhattan, who took over the case from her colleague Barbara Jones last month, rejected the SEC's argument that a recent court decision made a $150m note sale to Germany's IKB Deutsche Industriebank AG sufficiently 'domestic' to give her jurisdiction.
Monday's decision does not affect the rest of the SEC's lawsuit against Tourre, which arose from charges filed against him and Goldman in April 2010.
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