Crotone have yet to make a statement clarifying the situation, and while Nicola will not go into the reasons behind the exit, he says his departure will happen.
“It’s all true, I’ve made my decision and I’m not going back on it,” he told Gazzetta dello Sport.
“When I say something, I don’t beat around the bush. I think you know me well enough by now, you know how I am: I’m straight with my work and the decisions I make.
“It’s my own decision and I’m not going to go into it.”
Following a run of three straight defeats, the 44-year-old leaves the side two points and two places clear of the relegation zone in Serie A as they battle to beat the drop.
Rangers centre-back Russell Martin will miss Scotland's friendlies against Costa Rica and Hungary through injury.
Jonathan Walters is ready to continue his Republic of Ireland career when he returns to full fitness, according to Martin O'Neill.