A literary agent has told a court the authors suing over claims The Da Vinci Code copied their earlier work "were in danger of making fools of themselves".
Random House published both books at the centre of the dispute
Giving evidence at London's High Court, Patrick Janson-Smith also claimed plans for a Hollywood film of Dan Brown's novel prompted the court case.
"I thought the legal case was all a storm in a teacup," he said.
Michael Baigent and Richard Leigh are suing publisher Random House, claiming Mr Brown stole ideas from their book.
They claim Brown's best-selling novel "appropriated the architecture" of their work, The Holy Blood and the Holy Grail, published in 1982.
Both books, published by UK publisher Random House, explore the theory that Jesus married Mary Magdalene, that the couple had a child and that the bloodline survives.
"I didn't think Baigent and Leigh had a leg to stand on," said Mr Janson-Smith, referring to 2004, when the authors' agent said they intended to take action.
New Zealand author Michael Baigent is one of the co-claimants
"While I saw similarities between The Da Vinci Code and The Holy Blood and the Holy Grail, I never thought there was a copying issue to deal with," said Janson-Smith, former publisher to both parties.
He said the timing of the legal case appeared to coincide with the news of a big screen adaptation of The Da Vinci Code.
"They were most especially concerned that a film of The Da Vinci Code would jeopardise the chances of a film of The Holy Blood and the Holy Grail ever being made," Mr Janson-Smith told the High Court.
The film version of The Da Vinci Code, starring Tom Hanks, will receive its premiere at Cannes Film Festival in May.
Mr Brown, 41, was also in the witness stand, for a third day.
Dan Brown's The Da Vinci Code has sold 40 million copies worldwide
He denied allegations that he had borrowed, not only ideas, but specific words and phrases from The Holy Blood and the Holy Grail - arguing the phraseology was not identical.
The author has previously admitted to using the work while The Da Vinci Code was being written, but added it was used as one of several sources and did not use its central themes.
The case is expected to last until next Monday, while a judgment could take several weeks to be reached.