Moyes faced the media ahead of his side's pre-season friendly with the A-League All-Stars on Saturday.
"But for somebody following Sir Alex, that's the hardest thing to do. What he did will never be repeated.
"For anybody to do 25 years and for the trophies and the championships he has won, it would be incredible for anybody else to achieve that.
"It's a big job and one I am really looking forward to. I have been overwhelmed already.
"It's just a fantastic football club."