Barcelona coach Ronald Koeman rallied behind Lionel Messi after the Argentine delivered a vintage performance in Sunday’s 2-1 home win over Athletic Bilbao, hours after full details of Messi’s lucrative contract were published in the Spanish media.

Messi scored his 650th goal for the Catalans with a brilliant free-kick to put Barca in front against Athletic, while Antoine Griezmann struck the winner after Jordi Alba had scored an own goal to pull the visitors level.

Messi curled in a stunning free-kick in the 20th minute for his milestone goal as Koeman’s side recorded a fifth straight Liga win and moved above Real Madrid into second on goal difference with 40 points, 10 behind Atletico Madrid who have a game in hand.

The day had begun with newspaper El Mundo revealing the total amount Barca had spent on Messi’s last contract with the club, also declaring that the cost of the deal had “ruined” Barca by causing their current financial crisis.

“I don’t understand how anyone could link Messi to Barca’s ruin. He has spent years proving his quality and doing great things for this club, helping it win many important trophies,” Koeman told a news conference.

“Whoever published this had bad intentions and wanted to cause Barca damage. But we have to be united and focused, we have to forget about whatever has been published. Without Leo we couldn’t aspire to win very much.

“We have known for a very long time that he is the best player in the world, he has done so much for this club and is decisive. We have to respect everything Messi has done.”

Barca have threatened to sue El Mundo for publishing confidential information and said they were not responsible for leaking the contract to the newspaper, although Koeman said the club needed to get to the bottom of the issue.

“If this was someone from the club they cannot have a future here,” he added.