A glazed terra cotta relief by the Renaissance sculptor Andrea della Robbia came loose overnight from its perch above a doorway at the Metropolitan Museum of Art and crashed to the stone floor below, seriously damaging it, museum officials said Tuesday.

The shattered 15th-century sculpture, a 62-by-32-inch blue-and-white lunette depicting St. Michael the Archangel in a traditional pose, holding a sword and the scales of justice, was found early Tuesday morning by a guard on regular rounds.

Harold Holzer, a spokesman for the museum, said the sculpture, which had been on display over the doorway in the European Sculpture and Decorative Arts Galleries since 1996, may have done a back flip in the air as it fell, causing it to land relatively flat on its reverse side and sparing it “catastrophic damage.”

Officials said that a preliminary examination of the sculpture indicated that it could be repaired. Mr. Holzer said that large pieces, including the archangel’s face, were intact and that, late in the day, the conclusion was that the piece was “eminently restorable.”