The lawsuit, filed Thursday in San Antonio, seeks more than $1 million in damages against Charles Banks of Atlanta. It claims Banks secretly withheld 20 per cent of the return on Duncan's loan to Gameday Entertainment, for which Banks serves as chairman.
The suit also alleges that Duncan's signature was forged on at least two investment documents.
KENS-TV in San Antonio reports Duncan discovered the discrepancies last year while accounting for his assets as part of financial filings. Attempts to reach Banks for comment Friday were unsuccessful.