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.
After studying the drawing, historians now think that da Vinci at least played a role in the portrait's creation, even if he did not draw the entire thing himself.
Monna Vanna, ca 1515.
Based at the Louvre in Paris, where the Mona Lisa is held, they been examining charcoal drawing Joconde Nue.
However, after a series of tests at the Louvre Museum in Paris, experts now have strong reasons to believe that Leonardo worked on both.
According to curator Mathieu Deldicque the signs include the paper the sketch was made on.
"So many students of Leonardo have painted naked Mona Lisas or written about it, that we are nearly certain that Leonardo painted one", Mr. Deldicque said.
The drawing has a quality in the way the face and hands are rendered that is truly remarkable.
SUPPLIED A more familiar Mona Lisa
Mr Deldicque says the hands and body are "almost identical" and the portraits are the same size.
But as the eager speculation continues, Louvre conservation expert Bruno Muttin claims "we must remain prudent" about attributing it to the creative legend in 1519.
The biggest clue it might not be a da Vinci original is a hatching near the top right of the portrait - it's drawn by someone using their right hand, but da Vinci painted left-handed.
"It's a job that's going to take some time", Mottin said.
"It is a very hard drawing to work on because it is particularly fragile".
But Mottin said experts hoped to pin down the identity of the artist within two years, in time for an exhibition at Chantilly to celebrate the 500th anniversary of Leonardo da Vinci's death.
Around 20 paintings of nude women that bear a resemblance to Mona Lisa are exhibited or stored in museums across the world.