De Gea stood up to West Ham United striker Andy Carroll during last week's 2-2 draw.
"His first game last season was away from home against West Brom," Ferguson told MUTV.
"The referee felt he was a young goalkeeper, who was not used to English football. There was a laxity in terms of protection for him.
"That has passed now but Wednesday was beyond the pale.
"Let's be honest, there was an assault on him.
"But he stood up to it. He didn't let it affect him. He was brave and got on with his job."