A drawing of this quality has not come on the market since the war

Noel Annesley, Christie's

Dated at around 1481-1482, it is one of the only Da Vinci sketches left in private ownership and one of the earliest known pieces showing his fascination with horses.

Horse and Rider is a preparatory study for the artist's unfinished panel, The Adoration of the Magi, now in the Uffizi Gallery in Florence.

Controversy currently surrounds The Adoration of the Magi, with some 30 art scholars from the US, Britain and Italy signing a petition asking the Uffizi Gallery not to go ahead with a proposed restoration.

"A drawing of this quality has not come on the market since the war," said Noel Annesley, chairman of Christie's International Specialist Group.

Horse and Rider is a sketch of a work never completed

"Apart from the sheer beauty of the image - the horse, and the illusion of movement... it's quite unusual to find a drawing that is directly connected with a painting."

Da Vinci was a painter, sculptor, architect, theorist and scientist who continued to influence long after his death in 1519.

Horse and Rider has been part of the collection of Rhode Island inhabitant John Brown for 70 years.

Purchased at auction in 1928, it is now being sold on behalf of his son, J Carter Brown, the former director of the National Gallery of Washington.

Wide selection

The Old Master Auction includes a wide chronological selection of artworks from the high renaissance up until early impressionism, with about a quarter of the paintings by relatively unknown artists.

The latest work in the auction is early impressionist Jean-Fran�ois Millet's Evening, dated at around 1853.

The diversity of the auction is also reflected in the varying mediums. There are stained glass works by Ingres; tapestries by van Aelst; wall decorations by Giulio Romano; and engravings by de Gheyn.

Other lots of interest include a black chalk, pen and brown ink sketch of warriors and hippocamps [sea monsters] by French draughtsman and painter Nicolas Poussin.

The 175-lot auction is expected to fetch around �20m in total.