The lawsuit in federal court in Los Angeles said that Singer, 48, and entertainment industry executive Gary Goddard, 59, coerced the British man into sex acts as a minor with the promise of helping him in an acting career. The man was not identified in court papers.
This is the second lawsuit naming Singer ahead of the May 23 release of his film "X-Men: Days of Future Past," which is expected to be one of the year's top grossing movies.
Singer's lawyer has called the allegations in both lawsuits false and fabrications, and a bid to win money from the director behind other films in the "X-Men" superhero franchise. A lawyer for Goddard also denied the allegations, calling them spurious.
The lawsuit said the abuse happened between 2003 and 2006 and seeks unspecified damages.
The plaintiff's lawyer, Jeff Herman, also represents Michael Egan, who last month sued Singer, Goddard and two other entertainment executives over allegations that they abused him as part of an underage sex ring in Hollywood.
"He did this to support Mike, he realized he wasn't the only one this happened to," Herman said at a news conference. Herman specializes in child sex abuse cases and was successful in litigation against a former Roman Catholic priest accused of raping boys.
Singer will not participate in promotion for the 20th Century Fox's "X-Men: Days of Future Past" because of the lawsuits. The lawsuit filed on Monday accuses Singer of sexually abusing the plaintiff at age 17 in a London hotel room after the premiere of his 2006 film "Superman Returns."
In that incident, according to the lawsuit, Goddard is said to have gotten a "large, muscle-bound man" to smack the plaintiff after he had told Singer and Goddard to stop grabbing him in a sexual manner.
Goddard is also accused of having sex with the plaintiff at age 16 in London and convincing the plaintiff to send him naked photos of himself.
Goddard produced youth TV programs in the 1980s and 1990s and his company, The Goddard Group, has created attractions at theme parks, including Universal Studios.