Linklaters & Alliance is understood to be advising communications giant Vodafone on its hostile bid - estimated at more than $100bn (£62.5bn) - for Mannesmann and Orange.
The Lawyer understands the Alliance's London office and its German firm, Oppenhoff & Radler, have been enlisted to prepare the legal framework for the takeover.
Linklaters acted for Vodafone on its £39bn takeover of US telecoms company Airtouch this year.
Vodafone's share price was driven down on Friday due to market fears that its planned bid was overvalued. The company issued a statement via the London Stock Exchange saying it "continued to evaluate a broad range of opportunities but had reached no decision yet".
Linklaters refuses to comment on its involvement in the bid. Securities partner Clare Moulder, who advised on Vodafone's purchase of Airtouch, says: "There has been a stock exchange statement and I have nothing to add to that."
Head of corporate Anthony Cann says: "I couldn't possibly comment.
"If we were doing something it would be confidential information.
"As far as I am aware nothing has been indicated that they are or are not doing anything so I can't say whether we are doing anything."
Michael Caldwell, Vodafone's communications director, says: "This is purely market rumour and speculation and we never comment on that. There has been no action, reported or otherwise."
Mannesmann bought Orange last month for £20bn in a bid to ward off the long-rumoured bid from Vodafone by making itself too costly.
Bruckhaus Westrick Heller Loeber is Mannesmann's main German advisers. No one from the firm was available for comment.