The contract extension would ensure the 38-year-old remains in competitive action until and after the 2026 World Cup hosted by the United States, Canada and Mexico.
An official announcement is expected within the next two weeks, said the source contacted by AFP late Wednesday, and would mean Messi ending his career in the MLS.
Messi moved to Inter Miami in 2023 after an unhappy stay at Paris Saint-Germain, but the rump of his stellar career was spent at Barcelona, where he played from 2004 to 2021 after coming through the youth system at the Spanish giants.
At Barcelona, he won the La Liga title 10 times and lifted the European Champions League trophy on four occasions.
In 2022, he led Argentina to World Cup glory in Qatar and has expressed a desire to try to retain the trophy next year.
Messi was named the MLS Most Valuable Player in the 2024 season even though his team were eliminated in the playoffs.
In 2025, he became the fastest player to reach 40 goals in MLS history.
Keep track of Lionel Messi by following him in the Flashscore app - find out how to do that here.