Sampdoria, who have just been relegated from Serie A for the first time in over a decade, said the deal entails a cash injection of up €40 million to shore up the Genoa-based club's finances.
To finalise the takeover, the restructuring plan needs final approval from the club's creditors, a source close to the matter said, adding that talks with them were ongoing.
Hard-hit by the pandemic, Sampdoria have been for sale for over a year as part of a process aimed at repaying creditors of the club's former chairman and owner, who has been involved in a case of alleged bankruptcy.
A trustee has been looking after the sale process, with Lazard acting as advisor.
Radrizzani and Manfredi's proposal won out over a rival bid by Lille's owner Alessandro Barnaba, the club previously said.
Sampdoria enjoyed their heyday in the early 1990s when the Genoa-based club secured their sole national title with a team led by outstanding strike partnership Gianluca Vialli and Roberto Mancini.
Leeds also suffered relegation from England's Premier League last weekend.