Ferguson's book states Rooney came into his office "the day after we won the league and asked away" and revealed the 27-year-old's fitness had been an issue last season.
Moyes, who succeeded Ferguson in the summer, said Rooney was now "completely focused" and added that he had no concerns about him being unsettled by the book's contents.
He said: "I think Wayne is completely focused on his football, he has been since the first day back in pre-season. He's good in form, he's looking after himself. Alex Ferguson can do what he wishes - he's his own man."