Messi shocked Barca on Tuesday when he informed the team of his intention to leave this summer, despite having a contract until 2021. Barca responded by asking him to stay at the club he first joined as a teenager almost 20 years ago.
ESPN reported Monday that City have been crunching the numbers to work out if they would be able to sign Messi without breaching Financial Fair Play rules.
City have deemed the operation impossible in previous transfer windows, but several sources have confirmed that they have grown more optimistic following Guardiola's talk with Messi last week.
The two spent four years together at Barca between 2008 and 2012, and the Man City coach spoke to the Argentina international about the project that awaits him in England if he decides to make the move.
ESPN has also learned that high-ranking executives at City have spoken with the Messi camp recently, and they were aware that he had doubts about his Barca future before the Bayern debacle.
After Messi took the first step toward leaving Barca on Tuesday, City will have to decide if they have the money to make the deal possible without infringing UEFA's Financial Fair Play rules, which have been loosened because of the coronavirus pandemic.
Manchester City won their appeal to the Court of Arbitration for Sport (CAS) over alleged financial fair play violations on July 13 and are free to play in the Champions League next season.
A major factor will be knowing if Messi can leave Barca for free or if City will have to negotiate down his €700 million release clause.
Messi hopes to execute a clause written into his current terms, signed in 2017, that allows him to leave for free, unilaterally, at the end of each season. Barcelona, as reported by ESPN earlier this year, say the clause expired in June.
Paris Saint-Germain coach Thomas Tuchel said this week that Messi would be "welcome" at the French champions, and other clubs are expected to move for the six-time World Player of the Year if he is able to force an exit for free.