City defeat the Serie A leaders in last season's Champions League final.
Guardiola said: "We must not take anything for granted.
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"Now look at the quality of our opponents in England and in Europe. Look at Inter. They are flying to Italy and last year they said, 'we beat Inter in the final ...'"
"We knew how strong they were and look now, they will win the Scudetto if something strange doesn't happen, they win matches with a three or four goal difference and in the Champions League they beat an opponent incredibly strong like Atletico Madrid. So everything is difficult and this is why my message is not to take anything for granted."