The Sun says Blues owner Roman Abramovich is keen on giving new manager Carlo Ancelotti a big-name signing.
Reports says Atletico are not willing to sell Aguero for less than his £50million get-out clause.
The 21-year-old has also been linked with Manchester City and Manchester United.
Ancelotti said: “The market finishes on August 31 and if there is some possibility to improve the squad we can do it.”
