As posted by Fabrizio, Nottingham Forest has parted ways with it's manager Nuno Espirito Santo, these's was a tense situation at the club between him and them, I believe that's the main reason why he was sacked. Nottingham Forest has started off this season with a win, a draw and a lose in three matches. I believe that's one of the major trigger as to why he and the club management has fallen off and it resulted in a sack.
I'm just wondering who would be their next option, maybe they'll go for Ange Postecoglou, since he won Tottenham a trophy despite getting sacked, left for me I think Nuno would've still try to finish in the top six, I don't know what happened with the management, maybe they're not satisfied with the teams performance so far but it's still very early to make such decisions of sacking the coach.