United lost 3-1 at West Ham on Saturday to record their worst start in 29 years.
The Red Devils are almost out of the top 10 and nine points off the top of the Premier League table.
Players and staff were said to be openly discussing the prospect of Mourinho losing his job, as they made the journey back by train to Manchester on Saturday afternoon.
The defeat comes after a week in which United were dumped out at the third-round stage of the Carabao Cup by Championship side Derby and another public clash with Paul Pogba in training.
The club’s executive vice-chairman, Ed Woodward, had publicly stated that he will not make knee-jerk decisions and Mourinho will not walk away from a £15million-a-year contract.
United have also dismissed suggestions that they have already spoken to Zinedine Zidane over Mourinho’s job.
The Frenchman is available and understood to be keen on taking the post should United turn to him.
