For the first time since his six-year stint with United came to an end in 2009, Ronaldo is preparing to face them in the Champions League on Wednesday.
With Jose Mourinho now in charge of Real Madrid it is without question the tie of the round, with Robson finding it impossible to find tickets given the huge number of friends who have been in touch to ask.
Ronaldo seems certain to be a major influence given this season's return of 30 goals in 33 games for club and country, a tally that included a last-minute winner for Real when they faced Manchester City at the Bernabeu in September.
However, speaking at an event on behalf of Absolute Radio and official England supporter Mars, Robson believes Van Persie and Rooney will be of equal importance.
"Team tactics will be really important for United to combat Ronaldo," said Robson.
"You have to gang up on him as a unit rather than try and get one player to man-mark him because he could rip them apart.
"But I prefer to look at what United have, and in Van Persie and Rooney they have two of the best.
"As far as creating and scoring goals is concerned, over the past couple of seasons with Arsenal and Manchester United, Van Persie has proved he is right up there with Ronaldo and Lionel Messi.
"Real Madrid will be very aware of him.
"Also, Wayne played his best game for a couple of months at Fulham last Saturday.
"He has scored 10 goals in 10 games now and looks as if he is getting right into his top form at just the right time."
It will be intriguing to see how Ferguson uses his resources, especially as Danny Welbeck made such an impressive contribution against Liverpool recently.
The energy of Tom Cleverley or Anderson is likely to be used alongside Michael Carrick in central midfield as United look to block the holes Ronaldo can exploit, not to mention Mesut Ozil and Karim Benzema, Real's goalscorer in their draw at City in November.
For Robson, whose European career peaked with his starring role in that famous 3-0 win over a Barcelona side containing Diego Maradona in 1984 thanks to English clubs being banned in the aftermath of the tragedy at Heysel, it is a fixture that has really got the competitive juices flowing.
"It is going to be a fantastic tie," he said.
"You try and get a ticket. It is a nightmare.
"Both teams play good football and like to attack, which is great for the fans.
"Just thinking about it gives me a tingle."
However, despite his obvious bias, Robson freely admits he cannot call the outcome.
"These sorts of games are difficult to predict," he said.
"It usually comes down to the team that has a little bit of fortune or someone who scores an outstanding goal.
"There are so many great attacking players in either squad who can create goals out of nothing.
"But to try and predict who is going to win is impossible."