Messi's contract with the Catalan club came to an end on 30 June, and could have left the side on a free agent.
The new Copa America winner nearly exited Barcelona last term but saw his move blocked by departed club president Josep Maria Bartomeu and LaLiga president Javier Tebas.
And with Barcelona appointing new club president in the shape of Joan Laporta, keeping the six-time Balon d'Or winner remains his prime objective as he's also said to have been planning for a swap deal for other players to reduce the club's age bill after offloading Junior Firpo and Jean-ClairTodibo.
Having won the Copa America with Argentina, his first major title for La Albiceleste in many years as they defeated Brazil 1-0 in the final thanks to an Angel Di Maria's superb lobbed.
The 36-year-old is currently on holiday and is expected to sign the new deal with Barcelona soon.
Pep Guardiola's Manchester City and Mauricio Pochettino's PSG are said to be the two main clubs chasing for the signature of the Argentine wizard but Messi also wish to play in the American Major League Soccer one day.
Messi holds Barcelona's record scorer with 672 goals, winning 10 La Liga titles, four Champions Leagues, seven Copa del Reys.
In an interview with Sky Sports News, Spanish football expert Euan McTear revealed the reason to the delay of Messi's contract extension.
"The reason it's a five-year deal is that it is likely that Messi will play the next two years but it's a longer deal so that he stays linked to the club as an ambassador. But the talk is he might go to MLS after two years while still being paid by the club.
"It's a way for Barcelona to spread out the payment over five years. That's part of the reason he's been able to take such a massive cut of around 50 per cent."
