Barcelona midfielder Ivan Rakitic has admitted that he is "running out of things to write" on Lionel Messi's hat-trick balls.

Messi hit another treble for Barca in their 5-1 win over Espanyol on Sunday, with the hat-trick his 21st in La Liga.

"I'm running out of things to write on Leo's hat-trick balls," he told AS.

"I know I'm repeating myself but he's unique. He'll bring another ball for us to sign and I really don't know what to put this time."

Messi has scored hat-tricks in three of his last four games for Barca.