The painting has remained in the same private collection for three decades
A self-portrait of artist Lucian Freud sporting a black eye could fetch £4m when it is auctioned next month.
The re-discovered 1978 work is described by Sotheby's as the artist's "most important self-depiction ever to appear at auction".
Self-Portrait With A Black Eye is one of five works by Freud being offered at the London Evening Sale of Contemporary Art, on 10 February.
The auction also features work by Andy Warhol and Gerhard Richter.
Self-Portrait With A Black Eye depicts Freud with a swollen eye which resulted from a fight with a taxi driver in which the artist was punched in the face.
The work, which has never been displayed in public before, has remained in the same private collection for more than 30 years.
Cheyenne Westphal, Sotheby's chairman of contemporary art Europe, said: "Considering the sheer Herculean effort that Freud invests in his work... and the circumstances surrounding the inception of this rediscovered and illuminating self-portrait, the present is of the utmost significance to the oeuvre of this venerated artist."
Oliver Barker, Sotheby's senior director and international specialist in contemporary art, said the sale could beat the previous record held by a Freud self-portrait.
"The sale of this remarkable rediscovery, which exhibits all the psychological intensity and painterly virtuosity of Freud's most celebrated works, represents only the third time a self-portrait by the artist has ever appeared at auction," he said.
"Man With A Feather (self-portrait) was the last to be offered at auction and sold in these salerooms in 2005 for a record-breaking £3.7m - the price remains the record for a self-portrait for the artist at auction."
Also to be included for sale is Freud's 1981 oil on canvas Guy and Speck, expected to fetch between £800,000 and £1.2m, and Portrait of Christian Berard, which is estimated at £300,000-400,000.
Other important artworks in the sale include Richter's Abtraktes Bild, Warhol's 1964 work Jackie and Peter Doig's Saint Anton (Flat Light), estimated at £2-3m.