"It's not hard to see from the outside what it's been like," said Shaw.

"A lot of the time I've been here over the last few years it's been extremely negative.

"It can be quite toxic, the environment, it's not healthy at all. We need an environment that's healthy, that's positive, that's got good energy and happiness. When you have all those things, you feel free and you express yourself more.

"Ruben brings demands. Mentality is a big thing. He talks a lot about it.

"He demands 100% and doesn't want anything less. If someone's doing 85-90%, it's not enough. I think, especially this year, if you're not doing the right things, you won't play."

Shaw, 30, says the message must be reinforced by United's senior players, including himself.

"The more experienced ones need to be demanding more, day in, day out," he said.

"The levels in training, keeping to the times of when we're doing this or that, making sure no-one's coming late.

"The manager's not bothered. He doesn't care who the player is. That's how it should be. Whatever he wants, as players, we have to be delivering – and we are fully behind that."

Shaw did not mention United's 'bomb squad' - Rashford, Garnacho, Jadon Sancho, Tyrell Malacia and Antony - in his assessment and was not placing all the blame on those players, four of whom were not even at United for the second half of last season.

In a separate chat at a Premier League event in Chicago, the England defender did say there are "no stragglers in this group any more" and that Amorim had made it clear "everyone needs to put the team first".

However, United's longest serving player feels the aftermath of the final defeat in Bilbao took the club to such a bad place, it left everyone in Amorim's squad uncertain for what the future held.

"I wouldn't say I regret what I said but straight after the game, your head is hot, you say things and don't think about it," he said.

"A lot of people, after that final, and after that year, didn't know how the next season was going to look, we have to be open and honest about that. None of us were good enough.

"I had such an awful year as well. I was just fully angry about everything. That's why I did the interview and said what I said."