The 29-year-old midfielder played only two games in the last two years and has left the club after his contract expired on June 30.
Abou Diaby had his ankle broken by Sunderland's Dan Smith shortly after joining Arsenal from Auxerre in January 2006 and has been bedevilled by injury ever since.
Abou Diaby's injury curse struck again on Thursday when the Arsenal midfielder was ruled out for up to nine months after tearing the anterior cruciate ligament in his left knee.
English club's Arsenal manager Arsene Wenger said Wednesday that he was still looking to add more players to his team in the summer transfer window.
Forward Loic Remy has pulled out of France's provisional European Championship squad after failing to recover from a hamstring tear.