The Spaniard was also asked about United's summer spending spree, revealing that the German champions would not have entertained the idea of letting any of their players leave for Old Trafford.
"They didn't have enough money," Guardiola was quoted as saying by The Guardian. "I saw they spent a lot of money. It's part of the game. All of the clubs in the world want the players of another club."
On Manchester United's failure to qualify for the Champions League, the former Barcelona boss said: "It's a good lesson for the big clubs. They think: 'We are unbeatable and strong,' and they are not here. Maybe the next season they are out. That's why football is magnificent. Every single week you have to be ready. Every week you have got to show you are ready."
Bayern will be without Franck Ribery for their clash with United's neighbours Manchester City tomorrow night.