Nottingham Forest has really proved they're in form this season by them wining majority of their matches and by occupying the third spot in the Premier League. They've played 29 games, out of which they've won 16 games and drew 6, And currently they have not shown any sign of poor form from their last two matches. Therefore, this is really going to be a tough game though, facing Manchester United in this ecounter, I don't really see the easiness of Man Utd defeating Nottingham at their home soil, as the host team are doing all it takes to maintain their position and qualify for the champions league competition next season.
Nottingham Forest is quite close to winning the FA Cup and a ticket to the Champions League next season. After the international break, Nottingham Forest will face Brighton first in the FA Cup quarter finals, and then face Manchester United. Seeing Nuno Espirito Santo squad manage to hold Arsenal to a draw and beat Manchester City, I'm quite confident they will be able to make Manchester United suffer.
The Red Devils are 10 places below Nottingham Forest and the two teams are 17 points apart, I think that's enough reason why Nottingham Forest deserves to be favored, especially since they will be playing as the home team.