Chelsea have maintained their frenzied late activity in the transfer market as the deadline approaches by lodging a bid of around €20m (£16.6m) for the highly rated Porto wing-back Alvaro Pereira.

That opening offer falls short of the buyout clause in the Uruguayan's contract, which stands at €30m, and is likely to be rejected, with the Londoners braced for a hectic period of negotiations to follow.

The 25-year-old was a key member of André Villas-Boas's side which carried all before them domestically last season, and claimed the Europa League, and a first-choice for Uruguay as they won the Copa América in Argentina this summer.

Chelsea already boast Ashley Cole at left-back, with Ryan Bertrand and Patrick van Aanholt in reserve, but Villas-Boas is keen to replace Yuri Zhirkov, who moved to the Russian club Anzhi Makhachkala this month, with a player capable of playing either in defence or midfield on the left flank. Negotiations are ongoing between the clubs and should a deal be concluded, Chelsea's spending this calendar year would amount to around £120m already on six players.

That amount includes the Spain winger Juan Mata, whose £23.5m move from Valencia should be confirmed on Wednesday following the completion of his medical and could yet be extended with Chelsea still intent upon adding a central-midfield creator to their ranks. Should they continue to be frustrated in their pursuit of Luka Modric, the club will consider alternative moves for Raul Meireles at Liverpool or João Moutinho, another Porto player, before the deadline at the end of the month.