The centre-back has been a rotated player in Arsenal's defence this season, but his forceful display on Wednesday against Bayern Munich has led to deserved praise from the Arsenal boss.
“He was outstanding on Wednesday night,” Wenger told the official Arsenal website. “He has shown a bit more authority than usual and when he gets into that frame of mind, you can see he has outstanding qualities. It’s something I know he has but he needs that authority in his game to get his qualities completely out.
“He says that he was disturbed in his preparation [in pre-season]. In our final game in Cologne, he had a calf injury. It took him a long, long time to come back and after that he had many setbacks through the season.
“And every time he was close to coming back, he had another injury or sickness. He was sick a lot this year.”
Even though Wenger has been criticised for rotating his centre-backs, the Frenchman has defended his decision to keep his defence fresh.
“They [Koscielny and Mertesacker] do well together - it is true,” Wenger said. “I can’t see any obvious reason why Per and Vermaelen should not do well together.
“I have not analysed all the games they have played together because I have played Vermaelen and Koscielny together in some big games as well.
“You think that should work as well because they are two good football players. Because we want to play football they should work well - and one is right-footed and one is left-footed.”