The Portuguese coach has struggled in his first year in the job at Old Trafford but United co-owner Ratcliffe thinks that he needs an extended period to make a positive impact at the club.

Speaking on The Times' The Business podcast, the INEOS billionaire said: "He has not had the best of seasons.

"Ruben needs to demonstrate he is a great coach over three years. That's where I would be."

Amorim's insistence on playing a 3-4-2-1 formation has been criticised in the media but Ratcliffe claims that he is not interested in outside noise.

He said: "The press, sometimes I don't understand.

"They want overnight success. They think it's a light switch. You know, you flick a switch and it's all going to be roses tomorrow.

"You can't run a club like Manchester United on knee-jerk reactions to some journalist who goes off on one every week."

Ratcliffe has faced criticism for cutting jobs and perks such as free lunches for United staff but has stressed that these moves were necessary for the club's finances.

He explained: "The costs were just too high. There are some fantastic people at Manchester United but there was also a level of mediocrity and it had become bloated.

"I got a lot of flak for the free lunches, but no-one's ever given me a free lunch.

"There are two halves to a football team - there is the business side and the sports side. The biggest correlation, like it or not, between results and any external factor, is profitability. The more cash you have got, the better squad you can build.

"If you look at our results for last year we have the highest revenues ever. Profitability, the second highest ever. Those numbers will get better.

"Manchester United will become the most profitable football club in the world, in my view, and from that will stem, I hope, a long-term, sustainable, high level of football."