Guardiola told reporters after being asked about City's chances of retaining the title: "It will be easier, the hardest is to win the title for the first time, it is an amazing title for us but it is only one title."
However, Guardiola said his players should not feel relaxed, adding: "Winning the Champions League is amazing for the club but how many teams have won the Champions League once? A lot of teams, we haven't achieved the feat of winning the title once but we are undoubtedly proud".
Guardiola also said the trio of Jack Grealish, John Stones and Mateokovacic who all missed City's 3-1 win over West Ham with injury on Saturday would not feature on Tuesday, adding: "I think they feel better but they won't play tomorrow."
"I hope they play against Nottingham Forest on Saturday in the Premier League or the next games because we need that because we don't have a big squad at the moment, look how we have proven ourselves without them in recent games, hopefully they will come back soon because we need to compete."
City won last season, along with the Champions League and FA Cup, to win a historic treble of titles.