BRUSSELS/FRANKFURT/MILAN (Reuters) - Atlantia's ATL.MI 17-billion-euro ($20 billion) bid for fellow toll road operator Abertis ABE.MC won unconditional EU antitrust clearance on Friday as Spanish builder ACS ACS.MC looked to prepare a rival bid.

Toll road operator Abertis´ headquarters is seen in Barcelona, Spain, October 9, 2017. REUTERS/Eric Gaillard

ACS is working on a cash-and-share offer for Spain’s Abertis, which it plans to launch next week, sources close to the matter said on Thursday.

The European Commission said the Atlantia-Abertis deal, which would create the world’s largest toll-road operator, would not hurt competition, confirming a Reuters report.

Sources said on Thursday that ACS' offer was expected to be roughly half in cash and the rest in newly issued shares in German construction group Hochtief HOTG.DE, which is controlled by ACS.

The value of an ACS offer was not known.

Milan brokerage Banca IMI said on Friday a potential offer with no premium versus Atlantia’s offer would be unattractive given the quality of Hochtief shares compared to those of the Italian company.

“Abertis shareholders would be directly exposed to the less predictable construction sector and, strangely, would even be financing the offer as Hochtief would issue new shares potentially to be underwritten by Abertis’ shareholders themselves,” the broker said in a note.

Atlantia’s offer was formally launched on Tuesday, a day after being approved by Spain’s market regulator, and runs until Oct. 24.

People close to the matter told Reuters that Atlantia may consider sweetening its offer if a counter-bid emerged, depending on the price and structure of any offer.

Under Spanish rules, any alternative suitors have until Thursday to present their own bid for Abertis.

Atlantia is offering 16.50 euros in cash or 0.697 Atlantia shares for each Abertis share. But the offer is conditional on Abertis shareholders who own between 10 percent and 23 percent of the Spanish company’s capital accepting the share offer.

Stefano Fabiani, fund manager at Milan-based Zenit, said the Atlantia deal offered synergies which could offer shareholders upside further down the road.

“Atlantia’s bid is there and the price looks about right. Time is running out for any counterbid,” he said, adding the market was waiting for concrete news.

At 1028 GMT Atlantia shares were up 0.26 percent while Abertis shares were unchanged.

Though the offer has been described as “friendly” by Atlantia, shareholders in Abertis have not expressed a view on the proposal.

The board of the Spanish company must publish its assessment of the bid within 10 days of its start.

Abertis's top shareholder is Criteria Caixa, the financial arm of a politically connected and powerful banking foundation that controls Catalonia's largest lender Caixabank CABK.MC.

“Apparently, La Caixa would be willing to sell, but it wants a compelling case with a better price,” analysts at Mediobanca said in a note to clients.