The French international missed the Gunners' pre-season tour of Asia as well as their stint in Germany to have surgery to cure an ankle problem.
Gunners boss Arsene Wenger has confirmed that the 25-year-old will be sidelined for over two months.
"Abou had ankle surgery during the break," Wenger told the club's website.
"Normally he should be back eight to 10 weeks after his surgery, which means the end of August."
Diaby will miss the start of the Premier League season, including games against Newcastle, Liverpool and Manchester United.