Barcelona captain Sergio Busquets said the shock of Lionel Messi leaving the Spanish giants had yet to sink in as he thanked the Argentine for all he'd done for the club on Friday.

The six-time Ballon d'Or winner Messi had been expected to sign a new five year deal with Barcelona on Thursday but instead, after 788 games, is leaving the club at the age of 34.

"I'm still trying to digest the news," Busquets wrote on social media.

"I can only thank you for everything you did for the club and for those of us who were there with you over the years, me especially," said Busquets, who played alongside Messi in midfield.

"I shared so many moments with you, nearly all good ones, and I was lucky to grow up alongside you over 13 seasons. We will miss you."

Messi had reached agreement with Barcelona to sign a five-year contract with the trade-off that he earned 50 percent less per year.

But La Liga's financial fair play rules, which are expected to reduce the amount Barca can spend on salaries this season by some 200 million euros (235 million dollars), led Joan Laporta to conclude they were unable to afford the deal.

Paris Saint-Germain are expected to lead the chase for Messi but Manchester City, who attempted to sign him last year, could also join the bidding.