Diaby is set for his medical after agreeing on a five-year deal with Al Ittihad, which will see Villa bank £ 60 million.
He scored ten times in all competitions with six coming in the English top-flight, where he was a crucial part of Unai Emery‘s attack.
The 25-year-old helped Villa finish fourth in the table to help them secure a return to the Champions League for the first time since 1983.