The canvas’s entry in the catalog for the Wednesday sale here goes on for 10 pages and includes 20 illustrations. It says the painting is the “property of a private New York collector.” A symbol next to the lot number indicates that Christie’s has a financial interest in “Study for Self-Portrait,” but the details are unclear.

What Christie’s has not disclosed in the provenance is that the painting was up for sale at Christie’s in New York in November 2008, when it did not draw a single bid. The work was also the subject of a lawsuit, settled last July, filed in March 2009 in the United States District Court in Manhattan by a family trust led by the Connecticut collector George A. Weiss. The trust said that Christie’s had reneged on a $40 million guarantee, which is an undisclosed sum promised the seller regardless of a sale’s outcome.

That guarantee had been offered in July 2008, before the markets plummeted. But by September, after Christie’s had possession of the painting, it said it would no longer honor the guarantee because of the uncertain economy.

The painting was put up for auction anyway, and when it didn’t sell, Mr. Weiss’s family trust sued Christie’s for the $40 million it says it was promised. In next week’s sale catalog the estimate simply says, “on request,” although Christie’s experts are telling clients they believe it should sell for around £20 million, or about $31.3 million.

Mr. Weiss did not return phone calls seeking comment. Ivor Braka, a London dealer who is Mr. Weiss’s agent, said he was “unable to comment” on the settlement of the lawsuit.

In a statement Christie’s said it “is delighted to be offering this important work for sale next week in London following an amicable agreement with the client in 2011.”

The portrait depicts Bacon perched on a bed, body twisted from head to toe. It was only this year that Christie’s experts determined that the body was based on a photograph of Freud.

Christie’s is hoping to capitalize on the record prices paid for Bacon works in recent seasons. A 1976 triptych went for $86.3 million in May 2008 at Sotheby’s in New York, and a 1975 self-portrait brought $34.4 million at Christie’s in London in June 2008. But both sales occurred before the markets slumped, and some dealers believe that Christie’s is offering the painting too soon after its last auction appearance.

While nobody will reveal the details of Christie’s settlement with Mr. Weiss’s family trust — citing confidentiality agreements — some experts with knowledge of the lawsuit said they believe that Christie’s ended up giving the trust a figure close to the $40 million it was after. If that is true, then Christie’s, not Mr. Weiss, owns the painting, regardless of the catalog’s designation.

Again, Christie’s declined to comment.