Ozil has impressed during the London club's run of eight consecutive victories, demonstrating why Arsene Wenger's spent big to lure the Germany midfielder from Real Madrid.
The 26-year-old has not been consistent during his time at the Emirates Stadium, though, and his performances for Wenger's side have divided opinion.
Former Arsenal goalkeeper Lehmann knows Ozil has the ability to be a match-winner and has challenged the playmaker to rise to the occasion when it matters most and show his class on a regular basis.
Lehmann told Perform: "Arsenal bought him to win championships nationally and internationally. That should be his goal.
"He can't do that on his own but he should be the one making the difference in big games. He's got the potential but has to show it."
Arsenal face Championship side Reading in an FA Cup semi-final at Wembley on Saturday and are favourites to win the competition for the second successive season.
