I really don't know what to say about Chelsea anymore because this team even if it has massive talent , they really don't look like a team when they play and when they win , it's just from pure skill and not actually playing like a team. Today , they lost again and I think a new coach might come to Chelsea this Autumn to try and save the start of the season.
Simply say that Chelsea is weak team, don't be shy!! 
Having full of skilled players will get nothing if Chelsea can't play as a team, play with an effective strategy, and have good mentality. So, don't be so surprised if Chelsea can be defeated by a small team like Nottm Forest.
In the match against Nottm Forest, Chelsea players actually dominated much the match. They won 77% of the ball possessions and made 21 shot attempts. Sadly, Chelsea players have no accuracy in shooting, they only made 2 shot on target and no goal at all. Considering this, the problem looks not in the coach but on the skill of the players in shooting.