City have been banned from the Champions League and Europa League for the next two seasons and fined 30 million euros (£24.9 million) after UEFA found them guilty of committing "serious breaches" of financial regulations.
The Premier League champions overstated sponsorship revenue in accounts submitted between 2012 and 2016, according to European football's governing body.
UEFA also said City failed to cooperate with an investigation into the matter launched by its Club Financial Control Body.
The shock punishment will cost City an estimated £170 million in lost Champions League revenue and the club reacted furiously, immediately vowing to appeal to the Court of Arbitration for Sport (CAS).
"Manchester City is disappointed but not surprised by today's announcement by the UEFA Adjudicatory Chamber," a statement read.
"The club has always anticipated the ultimate need to seek out an independent body and process to impartially consider the comprehensive body of irrefutable evidence in support of its position."
But, while City urgently plan their appeal, the football world waits to see how Guardiola reacts to a punishment that could convince the Spaniard to quit the Etihad Stadium at the end of the season.
Guardiola reportedly has a break clause in his contract which means he can depart at the conclusion of this campaign should certain stipulations be met that satisfy the City hierarchy.
City officials were said to be confident that, despite an underwhelming season which has seen them fall 22 points behind runaway Premier League leaders Liverpool, Guardiola would honour a contract that currently ties him to the club until 2021.
But staying with City now European football could be off limits is likely to be a rather more unappetising prospect for Guardiola.
Whether the former Barcelona and Bayern Munich boss wants to stick it out at City will show how much he has grown to love the club since arriving in 2016.
Guardiola is close to City directors Txiki Begiristain and Ferran Soriano, who worked with him at Barca, but his ties to City's Abu Dhabi-based owner Sheikh Mansour might be frayed if there is no escape from the embarrassing ban.
Leading City to a pair of Premier League titles in record-breaking fashion and winning a domestic treble last term underlined Guardiola's enduring qualities.
However, he has failed to get past the quarter-finals of the Champions League with City and another daunting test lies in wait in the last 16 when they face Real Madrid later in February.
The most recent of Guardiola's two Champions League titles as a manager came way back in 2011 with Barca and his failure to add to that tally is the one blemish on his otherwise glittering CV.
The critics who crow that he can only win Europe's elite club prize with a genius like Barca's Lionel Messi in his team have nagged at Guardiola for years.
So the prospect of wasting two seasons waiting to return to the pursuit of his holy grail could be too much for Guardiola to bear, especially as rampant Liverpool look capable of keeping the Premier League crown out of City's grasp for years to come.
Asked about the potential for a European ban in December 2018, Guardiola had been optimistic, but that trust proved misplaced.
"We will not be banned. I trust in them (the owners)," he said at the time. "If it happens, because UEFA decide that, we will accept it and move forward."
Everything has changed now and reports immediately after news of the ban broke claimed the 49-year-old would consider his future unless City win the appeal.
Guardiola is already 7/4 with bookmakers to not be in charge of City before the start of the next Premier League season.
In a doomsday scenario for City, it might not only be Guardiola who could be weighing up his options if the ban is upheld.
Mansour may feel the damage to his reputation and to City's status is too much to take and could put the club up for sale.
City stars including Raheem Sterling, Kevin Be Bruyne, Sergio Aguero and Aymeric Laporte are unlikely to be impressed at being hauled off the Champions League stage through no fault of their own.
They may consider demanding transfers, adding another factor that could push Guardiola towards the exit door.