Shawcross was behind Gerard Pique and Johnny Evans in the pecking order at United, securing first team football with Stoke in 2008 after a successful loan spell under Tony Pulis.
He told the News of the World: "Pique has been fantastic for Barcelona, Evans is the next United central defender so I didn't stand a chance.
"If I'm honest they were better than me at the time. I was more like Nemanja Vidic, a brick wall kind of player. They were more cultured, especially Pique.
"Where I was brought up there as always something more. At United it's the way. When you're 12 years old the other academy players turn up half an hour early to do ball work and they stay half an hour after the session.
"It's always drilled into you from a young age and that's why they bring so many through.
"You can tell the lads who were brought up the right way, they don't want a day off."