Ital Gas Storage, 92.5% owned by Morgan Stanley Infrastructure Partners, will have a capacity of around 1 billion cubic metres (bcm) when fully operational and is part of a sector considered strategic by Rome.
"The government will be looking at the deal under its golden power prerogative when the parties notify them," one of the sources said on condition of anonymity.
Rome is preparing a decree enacting special vetting power to protect strategic assets, including gas storage, from unwanted foreign buyers.
Members of Italy's ruling 5-Star Movement and opposition League party last month called for caution in deals involving investment funds and the country's critical infrastructure.
The Macquarie bid values Ital Gas Storage at around 1.2 billion euros including debt of around 850 million euros, one of the sources said.
Macquarie, Morgan Stanley and Ital Gas Storage all declined to comment.
Macquarie, which already owns part of Italy's second-biggest gas transporter Società Gasdotti Italia, is targeting a series of infrastructure investments in Italy.
It is in talks to take stakes in broadband infrastructure group Open Fiber and Atlantia's tollroad business Autostrade per l'Italia.
Italy has around 18-19 bcm of gas storage capacity, most of it run by gas transport group Snam.
Ital Gas Storage has not disclosed when it will reach full operational capacity.
($1 = 0.8479 euros)
(Reporting by Stephen Jewkes; editing by Barbara Lewis)
By Stephen Jewkes and Giuseppe Fonte