July 30 (Reuters) - Manchester United ( MANU ) defender Luke Shaw has backed manager Ruben Amorim's uncompromising approach to improve the standards in the dressing room, saying the atmosphere had been "quite toxic" at times.

Amorim took charge at struggling United in November and demanded more commitment from the squad. He also froze out key figures like Marcus Rashford and Alejandro Garnacho, who were among five players seeking to exit the club in the close season.

"A lot of the time I've been here over the last few years it's been extremely negative," said Shaw, a United player since 2014, in an interview with the BBC published on Wednesday.

"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."

Amorim was uncompromising as he questioned Rashford's work rate, saying he would rather pick the goalkeeper coach than half-hearted players.

Rashford has joined Barcelona on loan, while British media reports have linked Garnacho with a move to Chelsea or Aston Villa.

"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 added.

United, who finished 15th last season and lost the Europa League final to Tottenham Hotspur, begin the new campaign at home against Arsenal on August 17.