"In recent days I've given lots of thought to what I could say and the truth is that I can't think of anything," said Messi who broke down in tears.
"Now, I have to say goodbye to all of this. I've been here my entire life, since I was 13. After 21 years I'm leaving with my wife, with my three little Catalan-Argentine kids... I can't promise you we won't come back because this is my home and I promised my children that."
Messi said he is not ready to leave Barcelona where he spent his entire career.
"This is really difficult for me after so many years, being here my entire life, I'm not ready for this and honestly last year with all the nonsense with the burofax I was convinced I knew what I wanted to say but this year is not the same."
He added that he gave everything for Barcelona from the first day until he left.
"I gave everything for this club for this shirt. I'm so grateful for the care that people have shown me. I've never imagined having to say goodbye because I never thought of it."
The Argentine superstar said that it was difficult to leave without seeing spectators who cannot attend the stadium due to the coronavirus outbreak.
"If I had imagined it, I would've imagined the Camp Nou full and being able to say goodbye properly."
Pure Barcelona product Messi, who came from the club's youth academy La Masia, became a free agent on July 1 when his contract with the club expired.
The negotiations between Messi and Barcelona failed due to financial obstacles while President Joan Laporta blamed Spanish La Liga's rigid financial fair play regulations for Messi's departure.
For his future, Messi said his potential move to PSG is possible despite the talks between him and the French club have not been finalized yet.
"There's nothing closed at the moment, but we're talking about a lot of things. After Barca's statement, a lot of clubs showed an interest."
Having made his senior debut in Barcelona in 2004, Messi led the Spanish club to earn 10 La Liga and four UEFA Champions League titles.
The six-time Ballon d'Or holder also won seven Copa del Rey, eight Spanish Super Cups, three FIFA Club World Cups, and three UEFA Super Cups.
Messi is also Barcelona's all-time top scorer with 682 goals.
