A 300-year-old viola is expected to be sold for £27m ($45m) - making it the world's most expensive musical instrument in history.
Sotheby's and Ingles and Hayday will be holding a sealed bid auction for the Macdonald viola in June.
It is one of just 10 surviving violas made by revered stringed-instrument builder Antonio Stradivari and the only surviving example of his golden period (1700-1720).
His instruments are regarded as among the finest bowed stringed instruments ever created.
Sotheby's said there has not been a Stradivari viola on the open market for the 50 years.
The record price for a musical instrument is held by the 'Lady Blunt' Stradivarius violin of 1721. It was sold for £9.8m to raise money for victims of the Japanese tsunami.
Vice-chairman of Sotheby's David Redden said: "Every field is defined by one outstanding masterpiece which casts its shadow not only on its own domain but far beyond. The instruments of Stradivari are in a class of their own among the pinnacles of human craftsmanship and the Macdonald viola stands at the unquestioned summit."
Violist David Aaron Carpenter will be playing the instrument at Sotheby's in Paris and New York in the run-up to the bid.
He said: "This viola represents the pinnacle of human achievement in instrument-making, and it is in incredibly good condition. Almost as though you ordered a viola from Stradivarius and 300 years later he handed it you."
Tim Ingles, director of Ingles & Hayday, said: "The finest of all Stradivari violas is generally agreed to be the Macdonald of 1719. It is immaculately preserved. No Stradivari viola has been on the market for the last 50 years so this is truly a once-in-a-lifetime opportunity."
The viola is being offered by the family of the late musician Peter Schidlof. Before that it passed through hands of many titled owners including Godfrey Bosville, the third Baron Macdonald in the 1820s.