It has been held since 1862 in the collection of Renaissance art at the Conde Museum at the Palace of Chantilly, north of the French capital.
Scientists at the Louvre in Paris today explained they think "the drawing is at least in part" by the mastermind himself. The museum's curators chose to conduct extended tests on the sketch after new preliminary research, and ahead of the 2019 exhibition, Mr. Deldicque said. Leonardo's oil painting Mona Lisa also known as La Gioconda remains one of the world's most recognisable and valuable works of art.
The drawing has a quality in the way the face and hands are rendered that is truly remarkable.
The portrait shows the woman with a similar pose to the Mona Lisa but her body is turned more to the side and her head is turned further over her left shoulder. "It is nearly certainly a preparatory work for an oil painting", he added.
Louvre conservation expert Bruno Mottin said "Monna Vanna" dates back to da Vinci's lifetime at the turn of the 15th century.
He told the Parisien newspaper that tests had already revealed that it was not a copy of a lost original.
Experts still believe they may need some more time to definitively attribute the sketch to Leonardo, who died in France in 1519.
"That's very interesting because the arms are the same as the Mona Lisa's".
"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.
Mottin told the paper his team hopes to confirm the artist's identity within two years, to coincide with the opening of an exhibition in Chantilly to celebrate the 500th anniversary of da Vinci's death.
About 20 paintings and drawings of a nude Mona Lisa exist in collections across the world but most have proved very hard to date.