One of the “finest sporting pictures ever painted” is expected to fetch more than £20 million when it is sold at auction.

George Stubbs’s painting of a racehorse on Newmarket Heath will be sold at Christie’s in London on July 5.

The work, called Gimcrack On Newmarket Heath, With A Trainer, A Stable-lad, And A Jockey, is part of a sale of old master and British paintings at the auction house. John Stainton, senior director of British pic-tures at Christie’s, said: “This is a truly exceptional example of 18th century painting which holds immense importance on many levels – as an old master picture, as a great masterpiece of British art, and as one of the finest sporting pictures ever painted.

“It is a great privilege for us to be able to work with this painting and to offer it at auction.”

Stubbs spent his early career as a portrait painter in his native Liverpool and York, before finding fame as a painter of horses.

He painted Gimcrack, one of the most famous and successful racehorses of its time, in 1765 for its owner, Viscount Bolingbroke.

The painting was last sold in 1951 when it made £12,600 and became part of the Woolavington Collection of sporting art.

It is being offered for sale now by the collection’s current owners.