"Following consultations with specialists, Abou will undergo surgery to repair the injury in the near future," a statement on the Premier League club's website said on Thursday.
"Abou is expected to be out for around eight to nine months."
Frenchman Diaby has been plagued by injuries at Arsenal, missing most of last season with ankle and calf injuries. In 2006 he fractured and dislocated his ankle.
Diaby's injury setback means Arsene Wenger is without several first-choice players in their efforts to secure a top-four finish in the Premier League.
Jack Wilshere is also sidelined for two weeks while Theo Walcott will not feature against Reading on Saturday.
