Ozil missed in defeat to Champions League opponents Bayern Munich.
Keown wrote in the Daily Mail: "There was a fantastic atmosphere at the Emirates and Arsenal made a terrific start.
"They troubled Bayern early on but Mesut Ozil's penalty miss could not have come at a worse time. It sapped away the energy and Arsenal took 10 minutes to recover, but the fans kept backing their team.
"Arsenal put in a titanic effort to try and stay in the game but with 10 men they could not keep out Bayern.
"It was the second penalty that Ozil has missed this season and he now has a 25 per cent career success rate from the spot - four taken, one scored.
"It's not a great record for a German, but it probably didn't help that goalkeeper Manuel Neuer was friends with Ozil at school. Maybe he saved the playground penalties, too."
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