The Premier League champions lifted the trophy for a third season in succession on Sunday (22.05.23) after a 1-0 win over Chelsea but Guardiola feels that European success is needed for his team to be heralded as one of the best of all time.
The City boss, who has won five Premier League crowns in seven seasons at City, told Sky Sports: "A fifth Premier League in six years, seven in 12, I could not imagine winning five in six.
"I have the feeling we've done something exceptional. It's something extraordinary. People know how exceptional it is.
"But to be considered one of the greatest we have to win the Champions League, otherwise it's not complete.
"You have to win in Europe, the Champions League, to be considered one of the best teams like Manchester United or Liverpool but also it's unfair to say if you don't win it, the Premier League doesn't make sense."
City's title had been confirmed by Arsenal's 1-0 loss to Nottingham Forest on Saturday (20.05.23) and Guardiola praised his team for overhauling the Gunners to win the title after they had trailed by eight points at the start of last month.
He said: "There's a tendency to underestimate. They are winners.
"We pushed Arsenal but they are exceptional. They should be proud of where they have come from. They have to sustain it, that is the reality, but for me they are winners.
"They made me think a lot what I had to do to beat them, and they did it to us. Our relentlessness and not giving up, and having the feeling that we had to win otherwise it would not be possible, helped us a lot.
"Similar to Liverpool in previous seasons, they took us to our limits."