Despite another stunning season for the 24-year-old Argentine, Antic believes that he is now a more sullen character.
"He argues with teammates and with referees' decisions," he told Com Radio. "This Messi has changed a lot.
"You cannot dispute his quality but his state of mind in the last few months has not helped his abilities.
"Messi is now intermittent. He doesn't help recover the ball, the defensive work starts when the play finishes."
Meanwhile, Barca coach Pep Guardiola is reportedly ready to leave the club and take a break from football.