On January 31, US District Judge John G. Koetl ruled that the case could not be brought to court because the relevant statute of limitations had expired.
Any accusation of breach of warranty and fiduciary duty against Christie's would have had to have been brought within three years of the 1998 sale, while any accusation of negligence would have to have come within six years - not the 12 years it took the work's consignor, Jeanne Marchig, to act.
The Geneva-based widow of artist Giannino Marchig, who restored the portrait 50 years ago, Mrs Marchig reacted indignantly, saying: "I only learnt about the Leonardo attribution in 2009. How could I have exceeded the statutes of limitation?"
She has since appealed against the ruling on the grounds that the statute of limitations has not run, and that she is entitled to trial by jury to present the evidence in support of her case.
The coloured chalk-on-vellum portrait was bought at Christie's in 1998 for $19,000 by New York dealer Kate Ganz, who sold it to Peter Silverman for around $21,000 in 2007. Since then a number of academics, led by Oxford University Professor Martin Kemp, have assigned it to Leonardo. It has been renamed La Bella Principessa and been valued by London dealership Simon Dickinson at £100m.
Mme Marchig sued Christie's for damages in May 2010 after learning of the new attribution, citing "the misattribution of a drawing (which) sold far below its actual value, solely because of the defendant's wilful refusal and failure to investigate plaintiffs' believed attribution".
Judge Koetl's 12-page Memorandum Opinion And Order ruled that "the plaintiffs' breach of fiduciary duty claim is untimely, unless they can demonstrate a basis for tolling the statute of limitations".
Mme Marchig's appeal will be filed on March 25, with Christie's due to respond on April 29 - before the case is heard by a three-judge panel, probably in May.
Christie's chairman Ed Dolman told ATG that "We genuinely feel that we've got the right attribution, and we stand right by that. The fundamental issue for us is that we don't believe this is a work by Leonardo".
As standard part of the appeals procedure, a court hearing of both parties' lawyers is slated for March 15, to consider a possible out-of-court settlement.
Mme Marchig is understood to be willing to meet Mr Dolman to discuss the matter personally, but Dolman says Christie's "have no case to answer - unless we see new evidence".
Might that be forthcoming? ATG understands that Professor Kemp has uncovered important new leads in his research about the book in which the vellum portrait is thought to have been originally bound.
By Simon Hewitt
