The man's attorney, Jeff Herman, said the lawsuit is being filed as a "John Doe" because the accuser does not want his name made public.
Herman also represents alleged victim, Cecil Singleton, whose claims against Clash, 52, led him to resign from Sesame Street, the New York Post reported.
A spokeswoman for the puppeteer denied the latest allegations, stating: “Mr. Clash believes this lawsuit has no merit.”
But the accuser's attorney said he will detail the case at a press conference later today. He told the New York Daily News his client connected with Clash over the internet via a gay chat room. Clash used the pseudonym "Craig" and claimed to be only 30 years old.