Ronald Koeman says there are people "that want to do damage to Barcelona and Lionel Messi" after the forward's contract was leaked to El Mundo.
Koeman was speaking to the press after his side's 2-1 win over Athletic Club in La Liga on Sunday but the majority of the questions focused on the leak.
"What came out in the press today was with malicious intent and wanting to do damage to a player that has done so much for Spanish football and for this club," Koeman said.
"Messi showed once again today that he is born winner who knows how to focus on the game despite everything else."
Koeman added: "We have to try and find out how Messi's contract's come out in the press. They are things that cannot come out. There are people that want to do us damage.
"If the leak is from within the club, that's very bad. We have to help the players, the coaches to win games. If someone from inside the club has leaked it, they cannot have a future at the club."
The El Mundo report related Barça's financial crisis with Messi's contract, which is worth a maximum of €555m over four years, although he won't earn that much in the end. The report even used the word "ruin."
Koeman continued: "I don't understand why they say he's ruined Barca ... He's spent years and years showing his quality as a footballer.
"We have to highlight what he's done for this club. He's helped make this club great and we have to stop with all this contract nonsense."