Messi has flourished under Guardiola, winning two Ballon d'Ors and scoring more than 120 goals since Guardiola replaced Frank Rijkaard to start the 2008-09 season.
Barcelona has won eight major trophies in Gurdiola's two full seasons and Messi says "the truth is, after everything he's created and how he's rallied the team around him, it's difficult to imagine" the club without Guardiola as coach.
The 39-year-old Guardiola's contract runs to the end of this season.
Barcelona leads Real Madrid by two points as it vies for a third straight Spanish title.
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