Champions Chelsea have eight matches in the final month of 2017 – with five of those being at home.
City, meanwhile, have a Manchester derby at Old Trafford to contest in December, a home clash with Tottenham and trips to Newcastle and Selhurst Park to follow.
“December is a very tough month. Maybe they [City] drop some points,” Courtois 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 and it’s hard for them to drop points.”