No one from Russells Solicitors was immediately available to comment. Gossage was still listed as a partner at the firm that made it clear that unmasking Rowling was an error and not a marketing stunt.
At the time, Rowling, 48, said it had been "wonderful" to publish without hype or expectation and to get feedback under a different name even if that meant some publishers rejected her work as they had when she first touted her Harry Potter books.
The novel was released last April to strong reviews but minimal sales. Once her involvement was known, sales rocketed, sending the novel to the top of best-seller lists.
"I feel very angry that my trust turned out to be misplaced," Rowling said in a statement in July. "To say that I am disappointed is an understatement."
The novel, about a war veteran turned private eye investigating the death of a model, was published by Little, Brown, which in 2012 published Rowling's first adult novel "The Casual Vacancy".