Despite reaching the last four for the first time in their history last season, Guardiola insists they are far from the finished article
For one of the most decorated coaches of all-time, boasting a 75 percent career win percentage and 21 trophies, Pep Guardiola's record of two wins from his last 11 away Champions League matches is an uncharacteristic stain.
Manchester City's long court of the Catalan was not just to dominate at home, but secure City's place amongst the European elite by winning the Champions League.
Despite reaching the last four for the first time in their history last season, Guardiola insists they are far from the finished article.
"If you ask me if we are ready to compete in Europe, then we are not ready," he said last month despite a stunning 10-game winning run to start his tenure.
That streak, though, was snapped on their first trip in the Champions League proper in a pulsating 3-3 draw at Celtic three weeks ago.
Guardiola summarised the madcap 'Battle of Britain' in a famously raucous Glasgow atmosphere as a "good test" of where City are away from home in Europe.
Yet, as he returns to the club that made him as a player and a coach in Barcelona on Wednesday, Guardiola and City will get a far better look into how far they have to go to be Champions League contenders.
"The last decade, the last 15 years they dominate football the way they play," said Guardiola after Saturday's 1-1 draw with Everton. "Barcelona is special (in) the way they play because it is a machine."
Much of that dominance and style of play is thanks to Guardiola.
His 2008-2012 vintage side that won 14 trophies and even more hearts for its mix of intense pressing and penetrating passing is widely regarded as the best Barca team of all-time.
However, the political machinations and media demands, not to mention two years of baiting by then Real Madrid boss Jose Mourinho took its toll.
"Four years as coach of Barcelona is an eternity," he said when announcing his resignation in April 2012.
"I am empty and I need to replenish myself."
He did so firstly via a sabbatical in New York and then three largely successful years at Bayern Munich that lacked a crowning glory - winning the Champions League.
That he fell that step short with Bayern is due to three visits to Spain in the semi-finals for the past three seasons. Each time he left defeated without even managing to score a goal.
Under his old teammate Luis Enrique, Barcelona have moved on too. A Lionel Messi-inspired 3-0 win over Guardiola's Bayern in 2015 allowed Enrique to equal his friend's remarkable achievement of delivering the treble in his first season in charge.
The style has been tweaked too. Whereas the midfield axis of Xavi and Andres Iniesta used to provide Messi as the focal point of the Barca attack, the Spanish champions can now call upon three of the deadliest strikers in the world.
Luis Suarez and Neymar complement Messi's skill set and give Barca a counter-attacking dimension not so prevalent in the Guardiola era.
"They are three amazing players in front," added Guardiola.
"They are amazing on the counter-attack and they have a good build-up, so they are a good team."
Guardiola will be warmly welcomed by the vast majority in the stands and his old charges on the pitch, if not in the presidential box where old political divides remain.
That has much to do with the reason why Guardiola has only been back to the Camp Nou one other time than Bayern's visit in the past four years.
Sitting next to his father as a fan rather than an invited guest, Guardiola howled in astonishment at a virtuoso Messi display as Barca beat City 1-0 in March 2015.
Only a series of outstanding saves from Joe Hart prevented more severe punishment for the City that night.
Having unceremoniously expeditated England's number one for another former Barca man in Claudio Bravo, the first cracks in the Guardiola reign may begin to form if Barca prove a gulf still exists between the two on Wednesday.