A source close to Chelsea owner Roman Abramovich has said a deal to bring Atletico Madrid star Sergio Aguero to Stamford Bridge is far from certain as the Russian billionaire is unsure he would represent value for money.

Various media outlets have been reporting recently that Aguero is set to join the Blues in January for a British record fee of between £40-50million.

The 21-year-old has been in impressive form for Los Colchoneros and has filled the void left by Fernando Torres in 2007, scoring 60 goals in 151 games since his move from Independiente.

After Chelsea successfully earned a reprieve on their transfer ban following the Gael Kakuta scandal, reports are rife Carlo Ancelotti will try and add the Argentine to his ranks in the New Year - viewing him as the ideal partner for Didier Drogba.

"Kun" impressed the Italian during the sides' recent UEFA Champions League meetings, scoring a fantastic brace against the Blues in a 2-2 draw at the Vicente Calderon.

However, despite reports that a deal was as good as done for the player, Chelsea owner Roman Abramovich is apparently far from convinced to part with such a sum of money for one player.

According to the Daily Star, a source close to Abramovich said: "Roman hasn't decided yet on Aguero.

"It is an awful lot of money to pay and he is not going to rush into it."

Although it is expected the current Premier League leaders will make an approach for Aguero in January, a deal is not a certainty as Atletico are unwilling to sell the player for anything less than £40million.

Aguero meanwhile, has said that he will not force a move away from Atletico, meaning that a switch to West London could become a very protracted one.