The terracotta model, which is about 12 inches tall and dates from the late 1400s, was found in a mouldy box in an antiques shop by an Italian art collector.
After subjecting it to extensive analysis, Roy Doliner believes it is the long-lost model for Michelangelo’s Pieta, the huge marble statue which depicts the Virgin Mary cradling the lifeless body of Christ.
Mr Doliner will unveil the discovery at a press conference in Rome on Thursday, when the model will be returned to the Italian capital for the first time in centuries.
It took three years to restore the tiny statue, which was covered in nine layers of paint and held together with bits of Scotch tape.
It was originally attributed by Italian art experts to Andrea Bregno, one of the most celebrated sculptors of the 15th century.
But Mr Doliner is convinced that the exquisite detail in the statue, its age and references made to it in later paintings, prove that it was instead created by Michelangelo to convince a wealthy cardinal to give him the commission for the Pieta, which he eventually completed in 1499.