Lawyer Marty Singer wrote in a statement that the director plans to pursue a countersuit alleging malicious prosecution and expects to prevail.
The lawyer's statement came hours after Michael Egan III appeared at a news conference and accused the director of abusing him when he was between the ages of 15 and 17. Mr Egan included the abuse allegations in a lawsuit filed in Hawaii.
The lawyer is not related to the director, who has directed most of the X-Men films and The Usual Suspects.
The director's latest film, X-Men: Days Of Future Past, is to be released next month.
Mr Egan said he reported the molestation claims to authorities at the time and does not know why charges were never pursued.
With his voice occasionally wavering, Michael Egan III described abuse he said he endured at the hands of Singer and others. He said he was plied with drugs and promises of Hollywood fame while also enduring threats and sexual abuse in Hawaii and Los Angeles over several years.
"You were a piece of meat," Mr Egan said of how he and other teenage boys were viewed at the home where he claims Singer abused him.
He sued Singer in Hawaii and is seeking more than 75,000 dollars (£45,000) on each of four accusations: intentional infliction of emotional distress, battery, assault and invasion of privacy.
Los Angeles Police Commander Andrew Smith said the department is looking into whether a report was made.
Marty Singer called the claims absurd and defamatory.
"It is obvious that this case was filed in an attempt to get publicity at the time when Bryan's new movie is about to open in a few weeks," said the lawyer.
The lawsuit is possible in Hawaii because of a state law that temporarily suspends the statute of limitations in sex abuse cases. Mr Egan's lawyer Jeff Herman said he planned to file additional lawsuits in Hawaii against other Hollywood figures he said abused under-age teenagers. The lawyer declined to state who else he planned to sue.
The lawsuit says Singer attended several of the parties and forced Mr Egan into sex, giving him drugs and threatening him when he resisted advances.
Mr Herman has made a career of representing victims of sex abuse, filing lawsuits against organisations such as the Roman Catholic Church and Boy Scouts of America. In 2011, he won a 100 million dollar verdict against a Catholic priest who was accused of molesting dozens of boys.