"Every player makes a weight. They come back on the 25th and I will be there controlling how many kilos come up, (to see if) they come fatty," said Guardiola, who is known for being strict about diet and conditioning.
"The moment they arrive after three days I want to see how they come back. They can eat but I want to control them. I have to make a selection for (December) 27 against Nottingham Forest.
"Imagine one player and now he's perfect but he will arrive with three kilos more. He will (stay) in Manchester. He will not travel to Nottingham Forest."
Guardiola, who once criticised England midfielder Kalvin Phillips for returning from the 2022 World Cup over his weight target, also said it was crucial for players to switch off and take a break from the relentless schedule.
"Next week I have holidays, being with family and with champagne," the Spaniard told reporters.
"I've learned from England, since I arrived, as much days (where you can) have a day off, you give them. The schedule is so tight and the players have to forget.
"The moment of the game they will be fresh in the legs. The players have to go with the families and forget football. It's good. For them to see the manager every day – that's so tough!"
City, who beat West Ham United 3-0 at the weekend, are two points behind leaders Arsenal after 17 games.