Arsene Wenger said Mesut Ozil did not appear to be himself while playing for Germany at the World Cup, and that the midfielder was negatively affected by the uproar at home over his photo with the Turkish president.
Ozil has been subjected to criticism at home following Germany's exit in the group stage in Russia as the defending champions lost to both Mexico and South Korea.
He had also been at the centre of a controversy in Germany before the tournament after the Arsenal star and Manchester City's Ilkay Gundogan posed for a photo with Turkey president Recep Tayyip Erdogan in England. Both players have Turkish heritage.
Wenger, who stepped down as Arsenal manager in May, told beIN Sports that he could tell from Ozil's play that the controversy had affected him.
"I know Ozil well, he's a fantastic, exceptional football player, but him and Gundogan suffered from what happened before the World Cup," Wenger said. "Ozil is a guy who needs support, he doesn't need controversy. And when I watched him play, I could feel that there were situations in the game where he could have moved forward, progressed, played more vertical.
"He played securely. I was thinking, 'Come on, that's not the real Ozil I know, the guy who can kill.' He did play all right, but I think he didn't play with complete freedom. He played a little bit with the handbrake in this World Cup."
Ozil signed a new long-term contract with Arsenal in January and will join up with Unai Emery's squad after his post-World Cup holiday.