The New York Post said Ulrich claims in his lawsuit he hasn't seen the 16th century painting -- which he believes is Parmigianino's "Rest on the Flight into Egypt" -- since he sent it to Sotheby's in 2005 to be appraised.

"The painting is in our system as having been returned," a Sotheby's representative wrote to Ulrich, offering as proof a release slip that says the auction house handed the work to Marco Grassi, the SoHo gallery owner entrusted by Ulrich to care for it.

However, the newspaper said court papers noted the release slip was for a painting with a different title and was never signed by Grassi.

"I asked Sotheby's, 'Would you deliver a multimillion-dollar painting without a signature?' They said, 'Yes,'" Ulrich's lawyer, Richard Ortoli, told the newspaper.