A 1941 Picasso to be offered at Sotheby’s tomorrow night with a $20 million to $30 million presale estimate was damaged while in the care of New York’s Acquavella Galleries, according to a lawsuit filed by the insurer of its owner, Ted Forstmann.

Forstmann, a financier who died last year, lent the portrait of Picasso’s lover, Dora Maar, to the Upper East Side gallery for a show in October 2008, according to the complaint filed in New York State Supreme Court in Manhattan.

“While in the care, custody, and control of Acquavella, the work was physically damaged,” American International Insurance Co. said in the October 2009 complaint.

The insurer paid Forstmann $7.5 million for damages to the painting, called “Femme Assise dans un Fauteuil,” according to the complaint. Sotheby’s “condition report” for the work, which the auction house makes available upon request, said it’s “in very good condition.”

Forstmann bought the work from Acquavella in 2001, according to Sotheby’s (BID) catalog.

“The surface is unvarnished and displays a rich and textured impasto,” Sotheby’s condition report said. “There is a two-inch repair below the figure’s neck where the canvas has been stitched. This restoration is of the highest standard and not visible to the naked eye.”