MILAN, Nov 9 (Reuters) - Nexi is happy to work with UniCredit to help one of its biggest clients achieve its ambitions in payments, but the contract between the two groups is "solid" and any change would have to benefit both, Nexi said on Thursday.

Italian payments infrastructure group SIA in 2016 signed a 10-year contract with UniCredit to manage cards and shop payments as well as cash withdrawal machines ahead of a being acquired by Nexi, which inherited the contract.

CEO Andrea Orcel months ago started a review of UniCredit's payments business with a view to managing it in a more unified way across the bank's various markets, prompting concerns among investors it might seek new partners, in a blow to Nexi.

Nexi finance chief Bernardo Mingrone told an analyst call on Thursday that the contract did not envisage the possibility of an early break-up.

"There is no option for either party to withdraw from this contract beforehand. And therefore there are no fees to be paid because there is no option, just to be 100% clear," Mingrone said.

While the contract is "very solid" and runs over the long term, Nexi is "very keen to help UniCredit achieve their ambitions in payments, which are growing," Nexi CEO Paolo Bertoluzzo added.

"Normally if you end up signing a new deal on top of an existing one that is solid it's something that you consider win-win for the company," he told analysts.

Orcel has said UniCredit would provide details of its payments strategy with its full-year results.

The bank's shop-owner payments business is one of the few assets that Orcel's predecessor Jean Pierre Mustier never considered parting ways with, even as he sold some 13 billion euros ($13.9 billion) in assets to shore up the bank's capital buffers.

Asked whether UniCredit might dispose of its merchant acquiring business, Bertoluzzo said he would be "very surprised" if UniCredit did anything with it.

"They want to invest more in payments not less," he said.

Orcel has been keen to grow UniCredit's fee revenue and payments is one of the few fee-yielding businesses the bank retains, after Mustier sold asset manager Pioneer and online broker Fineco.

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