Redknapp includes United captain Bruno Fernandes in his criticism, despite rating him the club's best player.
He wrote for The Sun: "I like manager Ruben Amorim but it will take years to turn them around . . . if it can be done at all. It has become a great club in name only.
"You’d look at the United of Fergie’s (Sir Alex Ferguson) day and see superstars everywhere. Amorim would love just one.
"Bruno Fernandes is the closest and even then no more than a place in the squad. He wouldn’t have a prayer of making the team.
"Who would you drop? Giggs, Scholes, Beckham, Roy Keane, Paul Ince, even Nicky Butt or Darren Fletcher? Not a chance.
"If Teddy Sheringham and Ole Gunnar Solskjaer struggled to get a game, Fernandes wouldn’t get beyond putting the cones down and handing out bibs."
United host Arsenal at Old Trafford later on Sunday.