Giggs has been appointed to David Moyesâ€™ backroom team along with another member of the famed â€˜Class of 92â€™ which Harrison was responsible for bringing through the ranks, Phil Neville.
Speaking at the annual McDonaldâ€™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 â€˜right, I am going to play golf every dayâ€™. He gets bored after five minutes if it is not football."
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