Giggs has been appointed to David Moyes' backroom team along with another member of the famed 'Class of 92' which Harrison was responsible for bringing through the ranks, Phil Neville.
Speaking at the annual McDonald's Community Awards, Harrison said: "Without doubt Ryan will be a success.
"He is a football nut. I am glad he is doing what he is doing.
"It would have been a tragedy if he had said 'right, I am going to play golf every day'. He gets bored after five minutes if it is not football."
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