Naturgy wants to split into two separately listed entities, with one focused on infrastructure and the other handling power generation and marketing.

"The last major deal was the entry of the Australian fund IFM, subject to an authorisation with conditions that we intend to monitor particularly closely," Ribera said when asked if the spin-off was "unwelcome".

Referring to IFM, which completed its stake acquisition in 2021, the minister said if Naturgy were to split, it would mean "this new player would be able join two different boards".

IFM's original intention was to appoint two board members as it aimed for a 17% stake in Naturgy but it was left with just one and a 10.83% holding. It now holds a 13.39% stake, according to the Spanish stock market supervisor.

The Australian fund also agreed not to sell off any assets beyond those already agreed by the board and it cannot delist Naturgy for at least three years.

Naturgy had planned to complete the separation of its infrastructure and energy business by the end of the year but current energy market disruption has potentially delayed the process.

Spanish media such as Expansion and El Confidencial have recently speculated that a spin-off could trigger changes in Naturgy's shareholder structure, allowing other players to join its capital.

Naturgy's shareholders include private equity firms CVC and GIP and Criteria Caixa, the investment holding company which is the main shareholder of Caixabank.

(Reporting by Jesús Aguado and Inti Landauro; editing by Emma Pinedo, Kirsten Donovan)