Premier League – Fergie: Ron Real move ‘mistake’
Ferguson feels the 23-year-old winger needs to stay at Old Trafford if he is to grow as a player.
However, Ronaldo has refused to commit himself to the club and Real Madrid continue to court him, even though they were reported to FIFA by United.
Ferguson remains clearly unhappy about the situation and for the second time on the South African tour found himself fielding questions about a player who scored 42 goals last season.
He said: “I have a responsibility for all my players and their futures are a big concern for a coach.
“If you were asking advice and it was your son, you’d give him the best advice possible on his career.
“I honestly believe that could be the worst thing he could do; going to Real Madrid.
“He’s 23 years old and he’s at a fantastic football club. It’s the best for him.”
Ronaldo signed a long-term deal last season in which United won the Champions League and retained their Premier League title.
He is currently sidelined for three months after an ankle operation following the European Championships.
Ferguson reiterated that he expects Ronaldo to play a massive role again next season.
He said: “The future is he signed a five-year contract last year and he has four years left.
“That’s definite. I know that, I’ve seen his signature. I feel I’m being strapped in and crucified here!
“Young lads can be twisted by the talk of money and the moves that are happening all the time in modern-day football.
“After the final in Moscow he was the happiest boy in the world. I think he knows genuinely where the best club is to be and that’s Manchester United.”