The size of the investment is still unclear, the source said, adding Lufthansa favoured a solution that would give private shareholders majority ownership of the Italian carrier.

The willingness of Lufthansa to take a stake in Alitalia could change a rescue plan that has been under discussion for months and which was expected to involve state-owned Ferrovie dello Stato, infrastructure group Atlantia and U.S. carrier Delta Air Lines.

(Reporting by Stefano Bernabei; writing by Francesca Landini)