Morrison has played just 12 minutes of Premier League football for the Blades since his free transfer move in the summer.
Maguire, who made an £80m move to Old Trafford in the summer, played against Morrison for the Blades in the 2011 FA Youth Cup final – and was knocked unconscious after a clash of heads with the mercurial forward.
And ahead of next Sunday’s clash between United and the Red Devils, Maguire admitted: “It has turned out strange.
“Ravel, when he was a young boy, was a top player. I haven’t played against him since [the 2011 final] but he’s got all the talent to be a top player and I hope he does really well with Sheffield United.”
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Maguire impressed throughout United’s run to the Youth Cup final, which ended with a 6-3 aggregate loss to the Old Trafford side – who fielded the likes of Morrison, Paul Pogba and Jesse Lingard in the two-legged final.
“It was just after half-time when it happened,” added Maguire, of his injury in the second leg at Old Trafford.
“I had a clash of heads with Ravel and actually got knocked out.
"It was the only time I’ve been knocked out in my career, touch wood. It was a nasty blow and I was in hospital overnight.
“Obviously it was disappointing to go off and not see the end of the game when the medals and trophy were presented.
“But then someone got in touch from Man United and checked I was okay. They sent me a Man United shirt, and just said: 'Good luck for the future, you’re a good, promising young player, keep your head down’ and so on."