Shaw's perceived weight issues and poor conditioning have dogged him throughout his four-year United career following his £27 million move from Southampton.
Realising he had work to do, Shaw went on a boot camp in Dubai with United fitness and conditioning coach Gary Walker at the start of this month.
The 23-year-old was put through gruelling twice-daily sessions, working in the gym and running on the beach in a bid to get himself in the best possible shape ahead of the new season.
Shaw is now in great shape physically following his gruelling personal training but, more than anything, he would rather his physique was not constantly judged.
Speaking to reporters at the Montage Hotel in Beverly Hills, where the Red Devils are based for their US summer tour, Shaw believes he is judged unfairly, partly as he has the same sort of natural body shape as United legend Wayne Rooney.
People can say I'm fat but I know my own body. I always look big because I'm bigger built. You could say a Wayne Rooney type of body.
The trip to Dubai illustrates his determination to compete with Ashley Young for United's starting left-back slot, and if a picture he posted on social media is anything to go by, Shaw has been doing all the right things.
I worked hard, and not just for them. I wanted to get in the best shape for myself and that wasn't my best shape.
Now I'm working harder than ever and for the first game of the season I want to look 10 times better than I did in that picture.
Once rated among the most exciting talents in English football, Shaw is entering the final year of a contract he signed in 2014.
I was unsure going into the summer what was happening. Of course, you would be unsure. You don't really know what will happen this season, whether it will be the same as last season or not.
One thing is for sure, I'm much fitter, more confident and a different person than I was last season. I've grown and learned a lot from the situations I've been in. I don't want to be in that situation again.
I want to play football. I'm not just here to pick up my salary and do nothing. I'm still just 23, have a very long career ahead of me and I want to play games.
I can't keep sitting on the bench and let my life go on, smoking a cigar and not doing anything. It's not me. I'm hoping it works out and I play this season here. If not, I need to look at myself and maybe find another solution.