An art collector is suing David Geffen for the return of a valuable Giacometti sculpture that the collector says was sold without his knowledge by his art adviser as part of an elaborate fraud.

In the court papers filed Tuesday in federal court in Manhattan, Justin Sun, a Hong Kong-based cryptocurrency entrepreneur and art collector, said the Giacometti sculpture, titled “Le Nez,” for which he had paid $78.4 million, was stolen from him and sold by the former adviser, named in the court filing as Xiong Zihan Sydney.

Ms. Xiong had helped Mr. Sun purchase the Giacometti at auction in 2021 and had suggested in interviews that the sculpture would become part of a collection to be owned by the APENFT Foundation, a platform she has said Mr. Sun was establishing to help bridge the gap between the art world and metaverse.

But lawyers for Mr. Sun said in court papers that he remained the owner of the work and that Ms. Xiong had forged his signature on documents related to the deal.

As part of the scheme, the court papers assert, the adviser appeared to have fabricated the existence of a lawyer who was purportedly overseeing the deal and then sent emails posing as the lawyer.

Ms. Xiong could not be reached for comment.

Mr. Geffen’s lawyer, Tibor L. Nagy, released a statement in which he characterized Mr. Sun’s claims in the lawsuit as “bizarre and baseless” and suggested Mr. Sun simply wanted to undo the deal.