Guardiola is into his second season in charge of City, having won three LaLiga titles – and two Champions Leagues – at the helm of Barcelona and three Bundesliga crowns with Bayern Munich.
But the Spaniard said the Premier League was not yet the most difficult, pointing to the records of English clubs in Europe.
Chelsea were the last English side to reach a decider in the Champions League, claiming the trophy in 2012, with Spain (six times), Germany (two) and Italy (two) the nations with finalists since then.
"I know you like to hear, 'it is the toughest one, congratulations'. You are the most viewed," Guardiola said, via the Mirror.
"Of course the Premier League is tough, so tough. But I would not say going to the [Santiago] Bernabeu, Camp Nou, [Athletic] Bilbao, Sevilla is easy.
"Because in the last decade, all the Spanish teams arrive in the Champions League and Europa League. Winning the Europa League – like Sevilla did three times in a row.
"The Premier League will be tough when, this is going to happen with five teams in the Champions League, they can achieve the last rounds.
"After we can say, 'that is the toughest league'. We have to make that step."
Guardiola's side claimed a dramatic 2-1 win at Bournemouth on Saturday to make it seven points from three league games, enough to sit fourth in the table.
Photo by: Getty Images Manchester City manager Pep Guardiola