The "very small fault", not visible to the naked eye, was discovered last November when the pounds 7.6m sculpture arrived in Madrid from Edinburgh. It was discovered, above the shoulder of one of the women, when the group was being inspected under strong lighting upon its arrival.
The work was on loan to Baron Heinrich Thyssen-Bornemisza, who gave pounds 800,000 towards its purchase. It is jointly owned by the National Museums of Scotland and the Victoria and Albert Museum in London.
The discovery alarmed both museums. Experts at the V & A rushed out to Madrid when they heard the news. And Richard Cook, its specialist conservator, travelled back with the sculpture to Edinburgh in a truck to monitor its condition. But the museum does not rule out the possibility that the crack may have always been present.
The disclosure could revive the debate about the risks of overseas lending, which last surfaced in Scotland when the Burrell Collection trustees in Glasgow unsuccessfully challenged a move by Glasgow museum officials to change the terms of that bequest to enable the collection to be shown overseas.
The Three Graces, commissioned from the Italian Antonio Canova by the Duke of Bedford at the start of the 19th century, has been the pride of the National Galleries for Scotland since its purchase in 1995.
A spokeswoman for the galleries said yesterday: "Detailed examinations of the statue in Edinburgh revealed that no further development of this fault has taken place."