Sir Alex Ferguson has told Cristiano Ronaldo that joining Real Madrid would be 'the worst thing he could do'.
The Manchester United manager 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.'
As United prepared to play the second match of the Vodacom Challenge against Orlando Pirates on Tuesday, Ferguson maintained he was happy with the squad at his disposal going into the new season.
He has yet to make any additions but has already made one bid for an unnamed player.
Last season he brought in Owen Hargreaves, Carlos Tevez, Nani and Anderson.
That strength in depth led to a notable double with Chelsea being defeated in the Champions League final in Moscow.
Ferguson said: 'We did a lot of stocking up last summer and bought players, who were at good ages.
'That was part of a policy we developed two years back, to bring in young players.
'We're delighted with how that's gone and we think they can progress even further.
'If you take the squad I had in Moscow; I had 23 players and those 23 players will still be there.
'It's a good strong squad so we're happy with it at the moment. Obviously we always try to improve but it can be difficult to get the right kind of players.
'There are always reasons why clubs don't want to sell, just like we don't want to sell our best players, so that makes things a little difficult. But I'm very happy with the squad I have.'
England defender Rio Ferdinand could return to the side on Tuesday after sitting out the draw against Kaizer Chiefs on Saturday because of a back spasm.
Ferguson said: 'His back is not so stiff at the moment. If he trains well, he will certainly start on Tuesday.
'He will want to get back into the action and I think it is important he plays.'
Ferguson added: 'We are expecting another competitive game and that is what we need at the moment.
'We played the Pirates two years ago and it was a good match. I think they have progressed so we will be tested.'