Shares of GVT, the Brazilian telecommunications target of a takeover attempt by two global rivals, posted on Friday their biggest tumble since late August, as suitors are seen as increasingly unlikely to raise their bids further.

Telefonica raised its offer for GVT by 5.2 percent on Nov. 4, seeking to trump a potential counterbid by French giant French media company Vivendi and seal a deal as early as next week. Vivendi's $3 billion friendly approach had yet to be formalized.

Under the terms of the counteroffer, the bid was upped to 50.50 reais a share, valuing the deal at about $3.9 billion, up from 48 reais a share, or $3.7 billion, previously.

Brazilian telecom watchdog Anatel ruled on Thursday that Telefonica can proceed with plans to take over GVT under a series of restrictions, quashing expectations that Vivendi could come forward with a sweetened bid, analysts and investors said.

It looks very unlikely that any other suitor would be ready to outmatch Telefonica's offer at this point, so in my view, GVT shares should begin converging with the Telefonica offer, said Alex Pardellas, an analyst with Banif Ixe in Sao Paulo.

Voting shares of GVT slumped as much as 4.4 percent earlier in the day, hitting 50.71 reais -- close to the Telefonica offer. They were down 2.3 percent at 51.80 reais in early afternoon trading on Sao Paulo's Bovespa stock exchange.

Vivendi, whose bid would not face any regulatory hurdles by Anatel, would have to offer a minimum 53.02 reais a share, equivalent to a 5 percent premium to the initial bid, to muscle out Telefonica.

But Pardellas, as well as some traders, said that would go against the French company's long-standing policies of only buying assets that do not risk its investment-grade debt ratings and of paying high dividends.

Telefonica's tender auction to buy out at least 51 percent of GVT was scheduled for Nov. 19.

(Editing by Gerald E. McCormick)