Moyes faced the media ahead of his side's pre-season friendly with the A-League All-Stars on Saturday.
But he was silent on the question of whether Rooney would be leaving Old Trafford for west London over the summer and instead chose to focus on the daunting challenge of following in Ferguson's footsteps.
"Anybody managing Manchester United would have a challenge, even Sir Alex," said Moyes.
"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.
"We dropped into Thailand on the way to Sydney and everywhere you go, if you are involved with Manchester United, everybody wants to meet the players and everybody wants to be involved.
"It's just a fantastic football club."