The Daily Mail says Ozil has been put on a weight-training programme as he struggles to fully adapt to the toughness of the Barclays Premier League.
Arsenal manager Arsene Wenger launched a staunch defence of his club-record £42million signing on Tuesday following criticism of recent displays - Ozil has not scored in his last nine matches and assisted just one goal.
"He thinks it's more physical here (in England) for sure and he is working on his body strength to deal with it," said Wenger.
"He works on strengthening his body in the gym. Mesut feels the pressure, of course. He knows a lot is expected when you are a big transfer.
"But he should not worry about that - just play, enjoy it and give his best - that's the best way to deal with it. But on the other hand, you must say he doesn't come from a small club."
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