City came from behind to beat Huddersfield 2-1 yesterday and record their 11th-straight league win.
Their gap at the top of the Premier League table remains at eight points and 11 points ahead of reigning champions Chelsea.
But to keep tabs on the runaway leaders, Conte thinks that he would need a January war chest.
“Manchester City’s path is incredible, no?” he said.
“I think Manchester City in this season is a strong team. Also last season, Manchester 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.”
Pep Guardiola was able to strengthen his side with the likes of Benjamin Mendy, Kyle Walker, Bernardo Silva and Danilo in the summer.
Conte meanwhile snapped up Alvaro Morata for £60million from Real Madrid.
Tiemoue Bakayoko, Danny Drinkwater, Antonio Ruiger and Davide Zappacosta took their summer spending up to just under £200m.
But Conte wants more quality when the window reopens if he is to reignite any kind of title defence.
Manchester City return to action at home to Southampton on Wednesday (8pm).
Chelsea meanwhile, host Swansea on Wednesday Stamford Bridge (7.45pm).