The 28-year-old has been at L'OM since 2006 when he signed from French amateur side FC Libourne.
He has gone on to become a full France international and helped Marseille finish second in Ligue 1 last season, ensuring a place in the group stages of the Champions League.
By qualifying for Europe's premier competition, Valbuena's contract at the Stade Velodrome was automatically extended through to the summer of 2017.
Despite being on a long-term deal, Valbuena has continued to be linked with a move away this summer, with Barcelona reportedly rivalling Premier League sides for his signature.
His agent, Christophe Hutteau, confirmed he has held preliminary talks with Barcelona, though the Catalans have yet to follow that up with a concrete bid.
"I can only confirm I had talks with Barca sport director Andoni Zubizarreta about Mathieu some time ago," he told La Provence.
"As his whole technical staff considers Mathieu to be a very good player, they all appreciate him."