The Citizens are set to take on Sparta Prague in the expanded group stages of the competition this week.
City beat Slovan Bratislava 4-0 in the competition last time around, but Sparta are also an unbeaten side.
“The truth is every week there are incredible games on a Tuesday and a Wednesday,” Guardiola told reporters.
“We have now many teams - 36 teams - and just eight qualify (automatically).
“So I’m pretty sure there will be extra qualification games for a top, top team.
“I’m pretty sure if we don’t close the games at home after our draw with Inter, we have three incredible tough away games, at Lisbon, Juventus and PSG.
“It is not easy. The games we have at home we have to close it, otherwise it’ll be difficult to finish in the first eight and that’s the target we want to achieve.
“Sparta have the same points as us.
“They played attractive football in Germany to draw against Stuttgart (in their last game) and created a lot of problems.
“I didn’t know Sparta Prague until the last two days and I have an impression.”