City beat West Ham United 3-0 on Saturday in their final match before Christmas, but Guardiola made it clear that standards would not drop during the short break. He confirmed that players were weighed before the West Ham match and met the required targets, and the same checks will be carried out when they report back next week.
"The moment they arrive after three days off, I want to see how they come back," Guardiola said. "They can eat, but I want to control them.
"Imagine one player is perfect now but arrives with three kilos more. He will stay in Manchester. He will not travel to Nottingham Forest."
Guardiola has long been known for his strict approach to fitness. In 2016, he removed several players from first-team training until they reached the weight levels he wanted. Former City full-back Gael Clichy has previously said Guardiola warned players to avoid pizza, some juices and certain heavy foods.
The City manager also addressed past comments about Kalvin Phillips, having previously apologised to the midfielder after describing him as overweight following his return from the 2022 World Cup in Qatar.
City are two points behind Premier League leaders Arsenal, who beat Everton 1-0 on Saturday. Guardiola's side face Forest next before travelling to Sunderland on New Year's Day.
Despite the win over West Ham, Guardiola said performance levels still needed to improve. He revealed that players had asked for Sunday's training session off, but he refused.
"The players asked me to have Sunday off and I said no, because they didn't play well enough," he said. "So Sunday recovery, train the guys that didn't play, and after three days off they have two days to prepare for Nottingham Forest."
Guardiola added that time with family over Christmas remained important.
"I've learned in England that as many days off as you can give, you give them," he said. "The schedule is so tight. When the game comes, they will be fresh in the legs."
Mikel Arteta said Arsenal won because his players stayed fully focused on the single task of beating Everton on Saturday, insisting that discipline and concentration were the key reasons they returned to the top of the Premier League.
Egypt captain Mohamed Salah has put his recent troubles at Liverpool behind him and is fully focused on winning the CAF Africa Cup of Nations, according to national coach Hossam Hassan.
Ruben Amorim has admitted Manchester United could be without captain Bruno Fernandes for some time after the midfielder was forced off during a 2-1 Premier League defeat by Aston Villa on Sunday.
Manchester United suffered yet another blow to their Premier League campaign with a 2-1 defeat to an in-form Aston Villa at Villa Park on Sunday evening.
