The midfielder endured a stop-start 2014-15 season for the Gunners after suffering a knee injury early in the season which ruled him out of action for three months.
Ozil scored four goals and notched up five assists for the Gunners as Arsenal finished third in the Premier League table and qualified for the group stage of next season’s Champions League.
He also helped Arsene Wenger’s men defend their FA Cup title.
However, former Arsenal goalkeeper Lehmann feels that Ozil still needs to prove that he can deliver in the big games for the north London club.
Lehmann told the Sun: “Everyone knows he can be a fantastic player. But you need to be a fantastic player in the big games. You don’t need to be a fantastic player in the small games and mediocre player in the big games.
“He can definitely do that but now he must prove it. You need to know how to think and how to programme yourself.
“Of course he can improve. You can’t get better on the day that you retire from football – but you can every day before that.”
Ozil has won consecutive FA Cup since joining Arsenal from Madrid back in the summer of 2013.
The Gunners kick off their Premier League campaign against West Ham on the opening day of the 2015-16 season.
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