The charcoal portrait is part of a collection at the Conde Museum at the palace of Chantilly, north of Paris.
Robertis performed a similar stunt before the Mona Lisa at the Louvre in April.
It had been attributed to the artist's studio, but after a month of tests at the Louvre, curators believe the "drawing is at least in part" by da Vinci, if not completely.
'It is nearly certainly a preparatory work for an oil painting, ' Deldicque said, suggesting there is a close connection to the Mona Lisa.
"We know the drawing was made during the lifetime of Leonardo da Vinci, we know that the paper was made in Italy, between Venice and Florence, and the third discovery is the high quality of this drawing in the face of the Monna Vanna and in her arms", Deldicque told reporters.
The nude charcoal portrait reflects a similar feel of the original Mona Lisa as the hands and body are nearly identical and the portraits are nearly the same size.
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"It is nearly certainly a preparatory work for an oil painting", he added, with the obvious inference being it is closely connected to the Mona Lisa.
The drawing is nearly the same size as the Mona Lisa and small holes pierced around the figure suggest it may have been used to trace its form on to a canvas.
Bruno Mottin, a conservation expert at the Louvre, told the newspaper the sketch is very fragile and pointed out the hatching at the top of the picture was drawn by a right-handed artist. The charcoal drawing, titled Joconde Nue, shows a topless woman who depicts a striking resemblance to the Mona Lisa.
Around 20 paintings and drawings of nude Mona Lisas exist in collections across the world but most have proved very hard to date. "Leonardo drew with his left hand", adding its analysis was a "job that is going to take some time".
"Very often, drawings are resumed, completed, transformed", said Patrick de Bayser, an expert in old drawings who works at the Galerie de Bayser in Paris and helps auctioneers value these drawings.
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