The England all-rounder paid tribute to Harris, who announced on Saturday that he is to call it a day because of a knee injury, and revealed the 35-year-old had been identified as a major threat in English conditions.
Asked how much of a loss he would be to the tourists, Moeen told Sky Sports: “Massive. He’s obviously a quality bowler and he will be missed in world cricket.
“He’s somebody who would have bowled really well in England, we felt, so it’s good for us. But it’s a shame that he’s had to retire.”
The series gets under way in Cardiff on Wednesday with anticipation mounting over a showdown which has produced some thrilling cricket in recent years.
But Moeen, who will provide a spin bowling option as well as batting in the middle order, is trying to take a more measured approach.
He said: “I’ve tried to stay away from it a little bit, to be honest with you, just put my head down and get my training done. But it’s quite natural for the Ashes and the whole nation is very excited.”
Captain Alastair Cook and his players will complete their preparations in south Wales over the next couple of days before launching their bid for revenge following a humiliating whitewash on their last trip Down Under last year, and for Moeen, the first ball cannot come quickly enough.
He said: “I feel good. I feel like I have trained quite hard lately, so I feel like I’m ready now and hopefully looking forward to Wednesday.”
New coach Trevor Bayliss put the players through their paces in a damp Sunday afternoon in Cardiff following last week’s get-together in Spain.