The 24-year-old centre-back has been a long-term target for the Gunners, with Arsenal boss Arsene Wenger thought to be a big fan of the Cameroon international.
Having arrived from Monaco in the summer of 2011, N'Koulou has established himself as a key part of Marseille's defence this term. But the French giants may have to sell before they can buy this summer, and N'Koulou - as one of the club's most sought-after players - could be among the first to leave.
Currently sixth in Ligue 1, Marseille will not be playing Champions League football next year. And without the financial boost provided by that competition, they could be struggling to make ends meet without player sales.
A €3.5m capture three years ago, Marseille would be looking for at least €15m to let him depart this summer.
They reportedly turned down a deal worth €13m from Napoli over the January transfer window, but they face a real battle to do the same at the end of the season.
Arsenal, Monaco and Borussia Dortmund are all still interested, according to France Football, which means there could be a scramble for his signature this summer.