"It's clear that the announced transaction would create a monopoly in cable content distribution and a de facto duopoly in fixed-line infrastructure in Germany," Chief Executive Markus Haas said in a statement.

"We therefore expect close scrutiny from the responsible competition authorities. If this combination is in any way approvable, then only under appropriately strict conditions."

Telefonica Deutschland, majority-owned by Telefonica of Spain, has a mobile-led strategy. That leaves it vulnerable to 'converged' mobile and fixed services offered nationwide by market leader Deutsche Telekom and, if the proposed deal goes through, Vodafone.

(Reporting by Douglas Busvine; Editing by Maria Sheahan)