The centre-back was shown a second yellow card by referee Maurizio Mariani on the 65th minute after bringing down SPAL striker Alberto Paloschi.
“The referees didn’t allow us to finish the game with 11 versus 11 and compete until the end,” the former Watford and Inter Milan manager told Italian broadcasters.
"It is an unfair expulsion, because it was a foul on N'Koulou. Instead they whistled against him and dismissed a fundamental player who will now miss the next match too.
"I’m very angry, because there was also a foul on (Andrea) Belotti in the penalty area and the decision was turned around."
Torino are 10th in Serie A with 31 points from 22 games, while SPAL are 14th with 22 points.
(Reporting by Alasdair Mackenzie, editing by Pritha Sarkar)
