Messi has long been linked with a reunion with Guardiola, with whom he won 14 of his 34 trophies at Barcelona during a four-year spell that saw the Argentinian ascend to a level that established him among the greatest players of all time.
Reports of a potential move to City intensified in August after the six-time Ballon d'Or winner informed Barca of his desire to leave the club.
Messi had been banking on being allowed to depart on a free transfer as previously promised by then-president Josep Maria Bartomeu, who subsequently informed him he would not be allowed out of the final year of his contract unless a fee was negotiated.
Guardiola reportedly met with Messi in Barcelona and told him City would be unable to enter such negotiations and advised him to see out his deal at Camp Nou.
With the Catalan's presence at the Etihad Stadium locked in until 2023, it could be argued that the groundwork is in place to pull off one of the biggest signings in history.
A marriage made in Barcelona
Under Guardiola, Messi played more games (219), scored more goals (211) and supplied more assists (79) in all competitions than he has for any other coach.
The Argentina star enjoyed his most prolific campaign in 2011-12 – Guardiola's last before leaving to take a sabbatical.
In just 60 appearances in all competitions, he accumulated an incredible 73 goals and 29 assists, both of which remain personal bests for a single season. He scored 50 times in LaLiga, the best all-time mark and one that is unlikely to be surpassed any time soon.
Across the entirety of 2012, he set a world record by scoring 91 goals – 79 for Barcelona and 12 for Argentina. His performances saw him become the first player to win the Ballon d'Or four times, and they came in successive years.
A disappointing start
Messi returned to Barca to work under Ronald Koeman after failing to engineer a move away, but 2020-21 has been far from a vintage season for him.
In his first nine games of the campaign he scored four goals, although every one of them came from the penalty spot.
He started on the bench for the visit of Real Betis prior to the international break due to concerns over his "freshness", but he came on for the second half and registered a double – ending his wait for a goal from open play with his second.
His minutes per-goal-rate of 195 is only good enough for 28th among players to have featured in at least five LaLiga games this season.
Could it actually happen?
Messi evidently remains unsettled at Camp Nou. Upon returning from international duty on Wednesday, he was asked for his thoughts on comments made by Antoine Griezmann's former representative Eric Olhats.
Olhats accused the club captain of overseeing a "reign of terror" at Barca and making Griezmann feel unwelcome following his arrival from Atletico Madrid for a fee of €120million in July 2019.
Messi responded: "I'm tired of being blamed for everything that's wrong at the club."
Guardiola has previously urged Messi to retire at Barca, but his change in circumstances at City may well alter his position on the issue.