The portrait, by photographer Michel Comte, shows a younger Miss Bruni gazing thoughtfully into the camera with nothing but her crossed hands to cover her modesty.
he pose, apparently in reference to the paintings of French neo-impressionist artist Georges Seurat depicting models, is expected to fetch around £2,000 when it goes under the hammer on April 10.
Miss Bruni and her husband, French president Nicolas Sarkozy, are to arrive in the UK on Wednesday for the start of their two-day state visit, and will be meeting the Queen and the Prime Minister, Gordon Brown.
Mr Sarkozy has faced criticism that his flashy, Rolex-wearing image is not in keeping with his function, and he had hoped that the visit would add some much-needed gravitas to his public persona.
According to aides, he is relying on the refinement of his 40-year-old Italian wife to wow the Queen and Duke of Edinburgh.
Educated in a Swiss finishing school, Mrs Bruni speaks fluent English unlike her husband, who has been taking intensive lessons to catch up and impress his hosts during the visit.
Christie's defended its decision to put the picture on sale, describing Miss Bruni as 'one of the most beautiful women in the world'.
'It's a work of art. It was shot in 1993 when Miss Bruni was a model and it's a tasteful nude portrait executed by a well known, respectable artist', said Milena Sales, spokeswoman from Christie's.
'Christie's stands by the works it represents to its clients, it doesn't censor or pass judgement on any content or subject matter. It's a perfectly respectable work of art.'
Text and image by The Telegraph, UK