Shawcross has revealed he was offered a new contract by United but opted to leave for first-team football.
He said: “Yes, I was offered a new four-year contract to stay at United but I didn't see a pathway through to the first team. I just wanted to play first team football and wanted to sign for Stoke, so I was then banished to train on my own at United before eventually signing for Stoke.
“I was absolutely terrified of [Ferguson], to be honest. Everyone was.
“But he was an unbelievable man-manager, and I put so much down to him and the people at Man United. Not only is it one of the biggest clubs in the world, it has huge standards off the pitch too, and that's something I am massively into – always have been."