By Ruth Bender and Inti Landauro 

PARIS-- Bouygues SA's rebuttal of Patrick Drahi's offer for its telecom unit sent chills through the French telecom sector on Wednesday as the prospect of the French market slimming to three mobile rivals from four moved further from the horizon.

Bouygues' board of directors on Tuesday unanimously decided not to pursue the proposal from Mr. Drahi's firm, Altice SA, which according to people familiar with the matter, offered to pay around EUR10 billion ($11.3 billion) for rival Bouygues Telecom.

The decision put the brakes on consolidation in the French market that key rivals, including Bouygues, Orange SA and Iliad SA have long clamored for and raises broader questions about the likely pace of deal-making activity in Europe. While Altice, which already owns the number two mobile operator in France, would have benefited from creating more cost savings in a merger, a deal would have rippled further too.

Low-cost operator Iliad SA would have been able to acquire some of Bouygues's spectrum to build out its network faster, while market leader Orange would have benefited generally from less competition.

Bouygues's reasons not to pursue the offer--including high execution risks, job losses and the potential for Bouygues to boost profits on its own--fell short for investors. "We believe these arguments aren't very convincing," said ING analyst Emmanuel Carlier.

Chairman and Chief Executive Officer Martin Bouygues defended his board's decision. "Not everything is a question of money," Mr. Bouygues told French radio, alluding to his personal attachment to the telecoms company he set up in 1994 after taking over the industrial conglomerate from his father.

Mr. Bouygues said regulators would have imposed heavy remedies in a merger, which would have made the deal unviable. "I don't see how Mr. Drahi could set up serious financing and at the same time assume all the remedies," he said. "The financing wasn't sorted out at all."

Altice hasn't officially responded to the collapse of the deal, but a person familiar with the matter said the offer was fully financed through a syndication of banks.

The decision is a setback for Mr. Drahi, who has been on a deal-making blitz on both sides of the Atlantic. Having snapped up cable assets in France over the years, he burst onto the mobile scene in a big way last year with his purchase of SFR from Vivendi SA. He beat Mr. Bouygues in the bidding and began cutting costs drastically, quickly lifting profit margins.

This appears to have played a role in Mr. Bouygues' decision. People familiar with the matter said the executive didn't want to sell to Mr. Drahi. Other people say Mr. Bouygues was concerned that he didn't want to take the risk of his telecoms unit suffering during a lengthy antitrust review, the cost of which he would have carried if the operation was blocked.

European regulators have allowed mergers in recent years that have lowered the amount of telecom rivals in countries such as Germany and Ireland. Operators have been eager to merge to save costs in heavily regulated and competitive markets. In all deals, antitrust authorities imposed remedies to assure that competition would be maintained, such as forcing companies to sell assets to allow new entrants to the market.

The proposed merger between Bouygues Telecom and Altice's Numericable-SFR would have been examined by France's antitrust authority, a process that could have lasted more than a year.

Mr. Bouygues rebuffed questions that political pressure influenced his decision, after French Economy Minister Emmanuel Macron in particular took a hard line against Mr. Drahi's offer. Bouygues, besides owning Bouygues Telecom and TV channel TF1, makes more than 70% of its revenues in the construction business, which often depends on government contracts.

Despite Bouygues's refusal, some analysts reckon the chapter of French consolidation isn't closed forever.

"Longer term, possibly one year from now, we could see M&A taking place, with either Bouygues or Numericable-SFR in a tougher spot," said Exane analyst Antoine Pradayrol.

Write to Ruth Bender at Ruth.Bender@wsj.com and Inti Landauro at inti.landauro@wsj.com

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