Royle knows Moyes from his time at Everton.
"This is not David's team," he told the Daily Star Sunday.
"The time to judge how he is doing at United will be at the end of next season when I am sure he will have his team.
"Yes, he did inherit the champions but I would argue that winning the title last season with this squad was one of Sir Alex's greatest achievements.
"What United should do now is back Sir Alex's judgment in picking David as his successor.
"You have to remember, too, that Fergie was given four years to win his first trophy in, admittedly, different circumstances.
"David came in to take over an ageing squad with a number of players moving into their 30s.
"Remember, Sir Alex had to bring Paul Scholes out of retirement to help this squad and Ryan Giggs, as great a player as he has been, should not be playing in the Premier League at 40 - particularly in midfield.
"This is not a vintage Man United squad. To judge him on this team is very harsh."
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