Earlier on Wednesday Italian financial daily Il Sole 24 Ore said an initial public offering for the brand that became famous for its trademark bright red dresses could happen between end-2017 and beginning of 2018.
In December 2015 the Qatari owners of the fashion house asked Rothschild to involve a number of banks in the listing, but the operation has been regularly postponed.
"The listing could be in 2018, but I can rule out that an IPO will happen in 2017," the source said.
In October, the chief executive of Valentino said the group still aimed to list on the stock market but that there were uncertainties on the timing of the operation.
Founded in 1960 by designer Valentino Garavani, the fashion brand was sold to Mayhoola for Investments, an investment vehicle with close ties to Sheikha Mozah, the second wife of Qatar's former emir, in 2012 for around 700 million euros.
By Eliza Anzolin, Writing by Giulia Segreti.