Diaby is nearing a first-team return after over a year on the sidelines with a serious knee injury, but despite his prolonged absence, Sagna believes that his compatriot can emulate the success of club legend Patrick Vieira if he can remain fit.
The 31-year-old told the club's official website: "To me, when he is fit, he is one of the best in the world.
"When he's at his best, he can play as well as Patrick Vieira did and as good as many players did. He can be useful for the team and he can be decisive."
Diaby has made just 178 appearances for the Gunners during his nine-year spell in North London.