The French operator announced plans to acquire fixed-line company Jazztel for £2.7 billion in September this year, but regulators have raised concerns that the deal will damage competition in the country.
The two companies offered concessions to the EU on November 13, but have since been deemed insufficient by the regulator.
The source told reporters that the Commission is likely to open an in-depth investigation today, and will reject a request from Spanish competition authorities to investigate the case.
