"I think Manchester City in this season are a strong team," said Conte. "Also last season, they were a fantastic team. Then, after the transfer market, they bought their first targets and then they have improved a lot.
"They can do this also in January maybe, in the future. For this reason we must be worried because if we want to compete with Manchester City we have to work and then make the best decisions in the transfer market."
City, who strengthened with the signings of Benjamin Mendy, Kyle Walker, Bernardo Silva, Ederson and Danilo, have taken 37 points from a possible 39 this season.
However, Chelsea goalkeeper Thibaut Courtois said a busy run of fixtures before the end of the year could see City start to drop points.
"December is a very tough month," he said. "We have to be there to keep on winning and hopefully close down on them, then towards the end of the season maybe overtake them.
"But at the moment they are the best team in the league."
Chelsea host Swansea City in the league on Wednesday while City welcome Southampton.
(Reporting by Hardik Vyas in Bengaluru; Editing by Peter Rutherford)
