Robbo had a pop at the pundits in the media over their criticism of Moyes.
He told the Daily Mail: "It was always going to be difficult for David as everyone wants to compare with Sir Alex but he is trying to be his own man. There are pundits throwing hand grenades into the mix as if they have first hand knowledge of what is going on behind the scenes but they don't know what they are talking about.
"You can be told about the enormity of this club and the task of replacing Sir Alex Ferguson but unless you are involved you can't judge. This place is different to any other club in the country.
"Chelsea think they are making ground and City are doing a very good job of building a squad but they are all still way behind United. That's not being disrespectful it's just this club is on a different scale with huge demands. You need to experience it before you can handle it and David can deliver the expectations of this football club."