The French international midfielder was recently released by the Gunners following the expiry of his contract, the former Auxerre man spending nine years at the club.
His previous five campaigns have been blighted by injuries, Diaby making just 32 Premier League appearances since 2010 and only one in the previous two seasons.
However, fresh reports from France's L'Equipe claim that Diaby has instead reached an agreement with Marseille, the 29-year-old flying to La Provence and holding reassuring talks with the club’s doctors.
Lack of transfer activity:
With Youssouf Mulumbu trading the Baggies for Norwich City, West Brom are light on midfielders and seemingly missing out on Diaby should see the club seek alternatives.
So far, James McClean has been the only addition to the Hawthorns this summer and there is a sense of growing frustration among supporters at their lack of activity as they head into the new campaign.