By Elvira Pollina and Giuseppe Fonte

MILAN (Reuters) -Italian state lender CDP and its partner Macquarie are at odds over the future of their loss-making fibre network operator Open Fiber, sources familiar with the matter told Reuters.

The standoff risks slowing down efforts by Italy's conservative government to combine Open Fiber with larger rival FiberCop, the network unit Telecom Italia sold last year to a pool of investors comprising KKR and Italy's Treasury.

CDP, which owns 60% of Open Fiber, is keen to merge the operator's assets with those of FiberCop to create a wholesale-only telecommunications network provider under state control.

But in the view of Australian fund Macquarie, Open Fiber needs to spin-off fibre assets in the most densely populated and profitable areas to ensure a smooth antitrust review for any combination with FiberCop, one of the sources said.

Macquarie, which spent 2.12 billion euros ($2.4 billion) to buy a 40% stake in Open Fiber in 2021, would be ready to take over those assets, the same source said.

Macquarie declined to comment.

However, CDP is not willing to hand over those areas as they represent Open Fiber's most valuable assets and are key to ensuring that the company is valued fairly in any deal with FiberCop, according to a second source.

Industry experts said those areas could be valued at 4-6 billion euros, including debt.

The structure of any potential deal needs to be negotiated yet and may emerge in a one-year timeframe, the second source said.

Any potential combination between FiberCop and Open Fiber needs to be cleared by European Union antitrust authorities.

CDP is confident Brussels could demand the sale of only a portion of Open Fiber's network assets in the most densely populated areas to preserve competition, the second source said.

FiberCop was valued at 18.8 billion euros in the KKR deal, when including some 9 billion euro in debts.

CDP declined to comment.

Open Fiber, which Italy's government tasked with rolling out fibre optic cables across the country almost a decade ago, posted a 364 million euro loss last year and forecast reaching a positive cash flow in 2028 at the latest.

($1 = 0.8817 euros)

(Reporting by Elvira Pollina in Milan and Giuseppe Fonte in RomeEditing by Keith Weir)