Marseille are currently sixth in Ligue 1 and some way off the pace set by the top three of Paris Saint Germain, Monaco and Lille.
Coupled with a disastrous UEFA Champions League campaign which saw them finish with zero points, N'Koulou says he cannot jump ship - despite Bayern Munich, Arsenal, Napoli and former club Monaco all being strongly linked.
"Leaving in the winter? I am no coward," he told France Football.
"I am not happy with what I have showed recently, so in such circumstances I won't leave.
"I owe a lot to l'OM who made me make a name for myself. It is very important for me to find again my best level first."