United, who kicked off eight points behind leaders Liverpool, already look out of the Premier League title race and a rift between the manager and Paul Pogba is overshadowing events on the pitch.
"If you want the truth I think it was honestly horrendous".
They took the lead after five minutes through Felipe Anderson and doubled it just before half-time when Andriy Yarmolenko's shot was deflected in by Victor Lindelof.
United's reverse, which came hot on the heels of their midweek Carabao Cup exit at the hands of Derby, means the Red Devils have their joint-lowest points total in Premier League history at this stage of the season.
"For me it was disappointing because I could not play against Chelsea because I was not 100 per cent", Arnautovic, who was linked to a move to Old Trafford this summer, said.
Notably, reports had emerged on Saturday that United held talks with free agent Zidane, who is interested in taking up the manager's role at United. The manager isn't on the pitch is he?
Second best: Luke Shaw (far right) says Manchester United were well below par in the West Ham loss.
"But the problem is, I don't think Paul Pogba is on his own if he's voicing these types of things". We're not very good in transition.
"We have to look at ourselves as players".
After a 2-1 home win against Leicester City on the first weekend of the season, Pogba indicated in post-match interviews that he could not speak his mind for fear of being fined by the club.
United's style is so out of step with the club's spirit and elite football in 2018, and has fed a situation where dressing-room sources say some of the team are nearly afraid to play at Old Trafford.
"At the same time, I feel that we need quality on the ball building up from the back and Scott McTominay has that quality". It was very poor from us.