The Blues have been persistently linked with a big-money move for the Argentine forward since the summer.
With Chelsea hopeful their current Fifa transfer embargo will be suspended following an appeal to the Court of Arbitration for Sport, rumours continue.
But, ahead of Tuesday's trip to Atletico, Ancelotti is adamant that Aguero is not set to be the subject of a bid.
QualityThe Chelsea boss said: "For his age he (Aguero) is one of the most important and best-quality players in the world.
"Aguero is very young, he is a fantastic striker and has a lot of quality.
"Every big club are looking at this player, but we are not thinking of buying anyone again at this moment."