The Frenchman has admitted the midfielder's departure is one of his saddest moments at Arsenal.
The Gunners released the midfielder at the beginning of this month, with his contract coming to an end and the decision taken not to extend it further.
The Frenchman had spent 10 years with the club, making 180 first-team appearances and scoring 19 goals, but a series of injuries ultimately ruined his time in North London.
As far as Wenger is concerned, though, the 29-year-old is the closest Arsenal have had to replacing club legend Vieira.
“He was the closest to Patrick Vieira we have seen here, with even a good offensive potential,” he told arsenal.com.
“In France, he’s regarded highly because every time he played in the French national team he made a difference. It is very sad.”
One of the saddest moments at Arsenal
Diaby’s failure to stay fit is certainly disappointing, given that when he was healthy, he proved to be the perfect player for the Gunners in that defensive midfield position.
Indeed, it is the area in the Arsenal side that most people claim Arsene Wenger needs to invest in the most, with the side having lacked a leader in that position since the days of Vieira and Gilberto Silva.
Francis Coquelin’s emergence last season could help to fill that void long-term, but Wenger admits seeing Diaby struggle to become the player everyone at the Emirates knew he could be ranks as one of the saddest chapters in his time at the club.
“It’s one of the saddest moments for us at Arsenal not to have had the opportunity to get the best out of Abou Diaby because of injury,” he added.
“I’m very sad because this boy is a massive and a huge talent. It’s sad as well because he didn’t deserve what he got. It’s sad as well because he’s a very serious player.”