Diaby's return to full fitness has lifted everyone at Arsenal this season.
“Arsenal have always had fantastic midfielder players,” Smith told talkSPORT. “Abou Diaby is one of them.
“Although he didn’t have a great game last night [against Montpellier], he’s a fantastic player.
“With those long legs he can rampage through the midfield, he’s a powerhouse. Diaby’s had a lot of injury problems but if he can stay fit, he’ll make a huge difference.”