Antonio Conte has warned Chelsea it "must be worried" by Manchester City's spending power ahead of the January transfer window.
City leads the Premier League table by eight points from Manchester United and is already 11 clear of third-placed champion Chelsea.
Pep Guardiola was able to bring in Benjamin Mendy, Kyle Walker, Bernardo Silva, Ederson and Danilo at great expense in the off-season.
And although Chelsea was also active in the market, signing Alvaro Morata, Tiemoue Bakayoko, Antonio Rudiger, Danny Drinkwater and Davide Zappacosta, there have been suggestions Conte is dissatisfied with the club's recent recruitment policy.
Asked about City's financial muscle and commanding lead, he said: "Manchester City's path is incredible, no? City in this season is a strong team, also last season, City was 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."
Chelsea lost Diego Costa and Nemanja Matic to Atletico Madrid and Manchester United respectively in the previous window, leaving Conte concerned about his options ahead of the packed festive schedule in late December and early January.
"I only ask for one thing – to have all my players available, because in our squad there are 16 senior players and I trust them," he said.
"It will be very important to have them available and then to have rotation. Last season was very difficult for me to find the best way but then we had a fantastic season.
"Now, this season, there is another challenge. We lost a lot of good players compared to last season, we lost two important players but at the same time we bought young players. In this league, we started with the two favourite teams, the two Manchesters.
"Chelsea, like last season, wasn't a favourite. Despite this, we want to fight, and I think we're trying to build something important for the present but especially for the future. It's important to be patient."
The Blues, who were held to a 1-1 draw against Liverpool on Saturday, host Swansea City on Wednesday.