Despite interest from Arsenal and Liverpool, City are hopeful of completing a deal for Van Dijk in January , and Conte believes that spells bad news for the competitiveness of the Premier League.
"Every team, every club, must pay great attention," the Chelsea manager said. "Because if a club like Manchester City takes all the best players, it will be very difficult for us to fight. Not only in England but in Europe.
"If they can do this, it is right for them to do this. We must pay great respect.
"When you have this opportunity to go in the market to spend a lot of money, I think it is right to do this.
"You must obviously be very good to spend your money in this way — sometimes you can spend a lot of money in a bad way.
"You must be clever to understand the positions, the roles you have to improve. In this case you must be very good.”
Van Dijk, 26, was left out at the weekend as Southampton lost 1-0 to Conte's Chelsea.