Messi had been expected to stay at Camp Nou, with the player admitting he had agreed to a five-year deal involving a 50% pay-cut.
But Barca, whose debts total way over 1 billion euros were unable to make the deal work within the frameworks of La Liga's financial fair play regulations - prompting a surprise U-turn announcement last week.
"Honestly, when the elections happened (in March), I spoke with (Barca president Joan) Laporta, we had dinner and after that I was convinced I would be staying," Messi said.
Lionel Messi has been with Barcelona for 21 years. Photo: AFP
"My contract was never the issue ... What I know is that I did everything I could. The club say it could not happen because of La Liga. I can guarantee you that I did everything I could to stay. Last year I didn't want to and I said that, but this year it was different."
French newspaper L'Equipe has reported the Argentine will travel to the France within the next couple of days to undertake a medical and finalise a deal with Paris St Germain.
While Messi did not confirm he would definitely join the Paris club he said his plans were to carry on playing as long as possible, adding he still harbours ambitions to win another Champions League trophy.
"As long as I go on being competitive and as long as my body responds (I'll carry on playing)," he told a news conference.
"As long as I can, I will carry on competing."
"I tried to behave with humility and respect and I hope that is what remains of me when I leave the club," said an emotional Messi as hundreds of fans, many wearing his No. 10 jersey, massed outside Barca's Camp Nou stadium to bid farewell to the player they called Messiah.
"This is all like a bucket of cold water has been poured over me and we are still coming to terms with it," he said through tears.
Messi, 34, who has been at the club for 21 years, becoming their all-time goalscorer with 682, broke down in tears before giving a speech and was greeted by a lengthy standing ovation from the media, current and former team mates and coaches in attendance.
-Reuters