Birmingham City boss Alex McLeish wants Nikola Zigic to toughen up.
McLeish signed the giant Serb for £6million from Valencia in the summer.
But the striker, 30, has struggled to adjust to the Premier League, scoring just three goals so far.
Big Eck said: "He's become more aggressive but I think he could get more aggressive still. Psychologically, it has been really tough for him.
"But now his stats are up and he works really hard for the team.
"The players respect him and he's a proud guy, I think it's a Serbian trait.
"He has a great mental toughness."
