The 29-year-old is searching for a new club after being released by the Gunners at the end of last season following a nightmare spell on the sidelines through various injuries and had been linked with a move to fellow Premier League outfit West Brom.
However, Marseille appear to have moved ahead in the race to sign the Frenchman on a free transfer and are set to offer a him a pay-as-you-play deal given his wretched injury record over the last couple of seasons.
Diaby was limited to just one appearance for the North London outfit last year as he was named in the starting XI for their Capital One Cup tie against Southampton at the Emirates Stadium in September 2014 and lasted for just over an hour before being replaced by Santi Cazorla.
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On his day Diaby was one of the best central midfielders in England, however, he was very rarely able to showcase his talents on a regular basis and return to France is likely to be his last chance at the highest level in European football.