The French midfielder, who has been plagued by injury setbacks during his eight-year career with the Gunners, is expected to be drafted into the squad for the visit of Ronald Koeman's side.
Diaby missed most of last season with anterior cruciate ligament damage, and Wenger believes that the fact that he is still able to compete at the highest level is testament to his inner strength.
"Diaby played 90 minutes at Villa Park for the Under-21s last week. He was with us at Villa Park again on Saturday and he will play against Southampton on Tuesday," the Arsenal boss told ITV Sport
"He is a giant, mentally. To do what he has done, with the severe injuries he had, he comes back every time, is dedicated and he deserves a lot of respect.
"I am a huge believer in his quality and I am sad as well that he couldn't show it more. If there is some justice, the future will be much better for him."
Diaby has made 181 appearances for the North London outfit.