Barcelona have agreed an improved deal with Argentinian star Lionel Messi that Spanish media are reporting could be worth up to to €25 million a year to four-times World Player of the Year.

No details of the new contract were disclosed, but the deal follows lengthy negotiations during which it was reported that the 26-year-old wanted to surpass Real Madrid's Cristiano Ronaldo has the best-paid player in the world.

Local media reported Messi would be tied to the club a further year, to June 2019, and would be paid €20 million euros a season plus a possible €5 million extra in performance-linked bonuses.

"FC Barcelona has reached an agreement to adjust the terms in the contract binding Leo Messi to the club as a professional first team player," Barca said in a brief statement.

“The revised and updated contract will be signed over the next few days,” they added.

Argentine Messi is Barca’s all-time top scorer with 354 goals in 424 official games and news of the deal is a boost for the club before Saturday’s La Liga showdown against Atletico Madrid at the Nou Camp, a game they need to win in order to retain the title. A draw would be good enough enough for Atletico to win.

Since the 26-year-old made his official debut in the 2004-05 season, Barca have won 21 titles, including three Champions League triumphs and six La Liga crowns.

He joined Barca’s academy at the age of 13 after a spell at Newell’s Old Boys in his native Rosario.

Speaking in his press conference ahead of the Atletico match, Barca coach Gerardo Martino welcomed the news of Messi's contract.

“It should give peace to him and especially to the club, who can continue to count on the best player in the world,” he said.