A judge overseeing the legal battle between Harry Potter author J.K. Rowling and superfan Steven Vander Ark has advised the pair to settle the dispute out of court.

Judge Robert Patterson urged the two parties to take their legal fight outside the courtroom, claiming the case would almost certainly end in years of appeals because it involves many unresolved areas of U.S. law.

The British writer sued Michigan, Detroit-based RDR Books for copyright infringement in 2007, in a bid to prevent the publication of Vander Ark's Harry Potter Lexicon, which was allegedly inspired by her novels.

Rowling has so far managed to stall the publication of the 400-page text, which was initially intended for release last November (07).

But the judge deems the case too complicated to be dealt with in court, telling the hearing on the third day of the battle in a U.S. District Court in New York, "I think this case, with imagination, could be settled".

The first two days of the hearing, which started on Monday, has seen emotional testimonies from both Rowling and Vander Ark.

The case continues.