The defender is a target for AS Roma.
Mazzarri said, “After the Wolverhampton match on Thursday, I sat the team down to show them the videos of the defensive errors we made, but N'Koulou didn't even want to watch it, saying his mind wasn't in the right place.
“I encouraged him and said we'd talk about it later. I called him again, but he said he didn't want to be called up. Out of respect for his teammates, I decided not to play him tonight.
“President Cairo has always kept his promises and he promised to me that we are keeping N'Koulou. He turned down important offers from big clubs.
“We wanted to give a sense of consistency to what we did towards the end of last season. I know that Roma tried very hard to sign him and we wanted to keep the player. I won't say more.
“Does he want to stay at Torino? You'd have to ask him that, all I can say is that we did everything to keep him."