"I sincerely hope that there will be a positive vote," Sergio Marchionne said just days before the key December 4th ballot, amid concerns a victory for the 'No' camp could spark Renzi's resignation and early elections in Italy.
The CEO of the auto giants told journalists however that he did not believe a defeat would produce the feared panic on the markets.
"It would displease me enormously if it were a 'No'," he said, but added: "The market will adapt".
"The reform is not perfect, we can always do better, but something has to be done," he said in reference to Renzi's plan to dramatically reduce the powers of the upper house of parliament.
Supporters say the reform would increase political stability in a country which has had 60 governments since 1946, but critics say it would strip Italy of vital democratic checks and balances put in place after World War II.
READ MORE: Everything you need to know about Italy's constitutional referendum
Photo: Emmanuel Durand/AFP