Ronaldo is now starring for Real Madrid.
Gill said: "Alex [Ferguson] and Carlos (Queiroz) in particular knew Ronaldo's mentality more than anyone else and Carlos told us that we would not be able to hang onto Cristiano for his whole career.
"He was that type of player and person.
"We had to make sure that we got the best out of him on the pitch, as well as making sure that we had a contract that made sure that we would get a good price for him.
"Everyone here knew that he would go sooner rather than later - we envisioned that six or seven years from when we bought him would be realistic.
"He's from southern Europe and very connected to his family. So that was how we viewed it."
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