Nicklas Bendtner flopped during seven years with Arsenal
The Denmark international - who once believed he was on a par with Cristiano Ronaldo and Lionel Messi - penned a deal with the Championship side earlier this month.
It came after disappointing spells at Wolfsburg and Juventus where he did little to live up to his own acclaim.
Wenger conceded he was shocked Forest swooped for the striker but hopes Bendtner can take the Championship by storm.
It was a surprise to me that Nicklas signed for Nottingham Forest, but at some stage Nicklas needs to restart his career
Arsene Wenger
"It was a surprise to me that Nicklas signed for Nottingham Forest, but at some stage Nicklas needs to restart his career," Wenger said.
"Of course he has a point to prove - he's playing at a level where he is not used to. But he did start his career at this level at Birmingham City with Steve Bruce, where he did very well. Nicklas is focused enough to show he can fight again.
"You have to adapt and we are in a job when we have to show we are able to put our effort in everywhere and compete. Sometimes when you are a player of his quality, you just need an opportunity. We know his qualities and he is a top quality player, but he needs to play.
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"The perceptions people have of him is that he is over confident but I don't think so. He was sometimes impatient when he was with us. He was disappointed not to get the chance and you can understand that.
"I am not here to judge people. Sometimes you manage to get it and sometimes we do not find the key. Then you have to leave the key to someone else who has the potential to find it. Nicklas could explain much better than I can about his career."
Bendtner is aiming to get one over on Arsenal when Forest host his former club in the EFL Cup tonight.
The Gunners haven't won the competition since 1987, where they beat Liverpool 2-1 in the final at Wembley under former manager and club legend George Graham.
