David Alan Brown, a curator at the United States' National Gallery in Washington, claims that the allegorical panel known as Tobias and the Angel displays the unmistakable brush strokes of the artist acknowledged as the greatest draughtsman who ever lived.
In a sensational piece of scholarship, Dr Brown argues that much of the figure of the young boy, and the details of the dog and the fish are clearly the work of the young Leonardo.
"It was a revelation," he said "The realisation was immediate as I looked carefully at the painting and my studies have only confirmed my belief."
During ten years of intensive research into Leonardo's early output and his time as a teenage apprentice in Verrocchio's renowned workshop, Dr Brown believes he has established that Leonardo contributed extensively to this painting. Since there are fewer than 20 works by the artist in existence, the discovery of a new painting is highly significant and likely to cause controversy among academics.
Martin Clayton, curator of the world's largest collection of Leonardo drawings at Windsor, is sceptical.
"Dr Brown is a cautious and reputable scholar and this is an interesting theory, but I don't believe it." He feels the dog is too ugly to be the work of such an exceptional artist.
The National Gallery concede that Dr Brown's suggestions are "interesting", but it has no plans to reattribute the picture.