When the Louvre in Paris announced that it had requested a loan of the Salvator Mundi ahead of its forthcoming Leonardo da Vinci show, it appeared that the world’s most expensive painting would finally be unveiled to the public.

But the museum has privately decided it will label the $450 million portrait of Christ merely as “from the workshop” of Leonardo - a move that would render it all but worthless and leave its Saudi owners humiliated, according to an art historian who has charted the painting’s extraordinary story.

Scholars continue to debate the provenance of the picture, which has been extensively restored.

Ben Lewis, author of The Last Leonardo, said: “The Louvre Paris have asked the Louvre Abu Dhabi if they could borrow it for their exhibition - that's official. But my inside sources at the Louvre, various sources, tell me that not many Louvre curators think this is an autograph [real] Leonardo da Vinci and if they did exhibit it, they really want to exhibit it as 'workshop'.

“So it is very unlikely it will be shown because the owner of this picture cannot possibly lend it to the Louvre Paris and see it exhibited as ‘Leonardo workshop’ - its value will go down to somewhere north of $1.5m.