The Benetton family, which already owns 33% of Atlantia, and Blackstone still need to get one final go ahead from Italy's market watchdog Consob before they can officially launch the bid on the stock market.
The Benettons and the U.S. fund, who have joined forces through investment vehicle Schema Alfa, have proposed a 58 billion euro buyout offer for the airport and motorway operator private to take it private by the end of this year.
The bid heralds a new phase for Atlantia which sold its domestic motorway unit earlier this year to draw a line under a political dispute sparked by a deadly bridge collapse in 2018.
($1 = 1.0213 euros)
(Reporting by Alvise Armellini; editing by Agnieszka Flak)