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 and led to him being dropped.
Moyes, who succeeded Ferguson as United manager in the summer, said Rooney was now "completely focused" and in good form - he has three goals and two assists in the Premier League, plus he has been excellent for England.
Moyes has not seen an advance copy of Ferguson book and said he had no concerns about Rooney being unsettled by its contents - and no issue with his predecessor going into print so soon.
He said: "None - 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 and playing well.
"Alex Ferguson can do what he wishes - he's his own man. Certainly everyone at Old Trafford would love to hear what he has to say, the supporters certainly would. He has great knowledge and I am sure a lot of people will enjoy reading it.
"I am sure I will when the time arises - I have not got much time in this job, that's for sure."
United face Real Sociedad in the Champions League at Old Trafford on Wednesday night and Moyes will be hoping Rooney can maintain his current form after some disappointing team results and performances this season, which the manager admits have been below par.
"We want to improve results, that's obvious," said Moyes. "We want to improve on our performance too, we gave the ball away too much in our last game and we have to do better when we are in possession.
"We have had periods of good play but maybe not continuously, which is something we have been working on in training."
Moyes confirmed that Belgium-born midfielder Adnan Januzaj has been added to the Champions League squad as a home-grown player and could make his debut in the competition tomorrow.
The 18-year-old signed a new five-year contract last week and Moyes said: "He is now available [for the Champions League] by the way his date of birth works. He's an exciting young player making good progress all the time and he someone who is going to play a big part in the future of Manchester United, he's an exceptional talent."
Four key players were absent from United's training session ahead of the Real Sociedad match - Danny Welbeck, Tom Cleverley and central defenders Nemanja Vidic and Rio Ferdinand, though Moyes said Welbeck and Cleverley had a chance of being fit for the game.
Jonny Evans is likely to play in central defence and the Irish international admitted the team has to eliminate some sloppiness from their play.
Evans said: "We are disappionted, we watched part of the [Southampton] game back and it was clear our performance was not up to scratch, especially in possession, giving the ball away and being quite sloppy.
"Being Manchester United we want to control games a bit better than we did against Southampton.
"As players we know we have not played well enough as individuals and as a team and looking at ourselves we want to make sure we raise our level and produce better performances."