The denial comes after the Italian daily Il Fatto Quotidiano on Sunday claimed Renzi spent €600,000 - purely on dinners - within five years.
Renzi responded by writing a text message to journalists at the paper, saying: “I was the first person to put my expenses online in Italy. Whenever I ate with my family and friends I paid from my own pocket.
"All my expenses between 2004 and 2013 have already been thoroughly examined by the Court of Audit."
However, the paper – and many opposition MPs - have argued that Renzi's expenses published online are just general figures, and not itemized accounts.
The Court of Audit has now opened a case into the premier's expenses during the time he was mayor and president of Florence.
The damning allegations emerged from an interview with the owner of a Tuscan restaurant, Da Lino, located just behind Palazzo Vecchio. It was a favoured spot for Renzi during his Florence days.
“He was never alone,” said the restaurant's owner Lino Amantini. “He used to bring anybody and everybody. If you had any idea of how many meals, parties, lunches and business dinners there were. There were an infinity.
“I sent the bills directly to the council. Since Renzi left Florence for Rome my takings have dropped considerably,” added Amantini.
But since being interviewed by Il Fatto, Amantini has performed a spectacular U-turn about the comments.
On Monday, he told reporters in Florence that he had never made those statements and that he was not prepared to speak to any journalists.
Claims of Renzi's extravagant dining habits come just days after the Ignazio Marino, was forced to quit as mayor of Rome over an expenses row involving a mere handful of dinners that had been charged to city hall over his 28-month tenure.
Meanwile, on Monday Renzi's father, Tiziano, was told that further investigation was needed into a bankruptcy claim he made in 2013 to establish whether or not it was fraudulent.