Arsenal’s loss to Nottingham Forest on Saturday ensured City wrapped up a third straight title win, and they sealed the achievement in style by defeating Chelsea 1-0 for their 12th consecutive league win, skysports.com reported.
City hope the Premier League will prove the first leg of a treble, with the FA Cup and Champions League finals to follow next month. They face United in the FA Cup final on June 3 before meeting Inter Milan a week later as they chase a first Champions League crown.
Guardiola, who won the European competition twice as Barcelona manager, said: “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.”
He added: “Of course, it makes sense, of course it’s important. It’s every day, every week. This club won five of the last six but six of the last 10 and seven of the last 12. It’s amazing.
“It can be unfair that you need to win the Champions League to give credit and value to what you have done but we have to accept it. It is good.
“A long time ago, people did not say I had to come here and win the Champions League but after what we have done, I know it will not be complete if I do not win the Champions League, if we do not win the Champions League.
“But sometimes training with this pressure is so nice. It is necessary. We talked to each other a lot, [saying] we have to do it.
“At the same time, if the club continues in this way, sooner or later we will do it. But we are there so we have to try.”
Guardiola also insisted Manchester City’s latest Premier League title success should not be demeaned by suggestions Arsenal ‘bottled it’ in the run-in.
The Gunners had led City by eight points as recently as last month but their form deserted them at a crucial stage.
Guardiola, however, paid tribute to his former assistant Mikel Arteta’s team after City celebrated their triumph with a 1-0 victory over Chelsea on Sunday.
Guardiola 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.
“With the relationship I have with Mikel - congratulations for what they’ve done. He’s brought them back to what Arsenal was in the past.
“Similar to Liverpool in previous seasons, they took us to our limits.”