Ronaldo's 50th-minute strike sealed a 5-0 aggregate triumph over Tottenham which ensured that Madrid will face Barcelona in the semi-finals.
If Jose Mourinho's side were to progress and Man United beat rank outsiders Schalke then Ronaldo would come up against his former team in the Wembley final on May 28 - and he admitted he would be 'happy' if that was the case.
Winner: Cristiano Ronaldo (second right) celebrates his goal against Tottenham
'Of course I would be very happy if I played against Manchester because I played there for six years, but let's see what happens. The final is a long way away,' he said.
If the two clubs were to meet it would represent a first appearance for Ronaldo against his mentor Sir Alex Ferguson and his former club, who he left in 2009.
But Ronaldo insists he is fully focused on his side's Champions League clashes with Barcelona on April 27 and May 3.
'It will be fantastic,' said Ronaldo. Madrid lost 5-0 to Barca in November, but Ronaldo played down talk of revenge. 'I don't like the word revenge - it will be interesting not just for us players but for the supporters and everyone who loves football.
Red devil: Ronaldo spent six years at Man United
'It will be interesting because at the moment we are the two best teams.'
'The games will be very, very difficult. We are going to play against one of the best teams in the world, which is Barcelona,' added the Portuguese international.
'We have to think it is possible because they are not from another world - they play football like the very best teams, but we are also strong.'
The two clubs face each other four times in just 18 days. They meet in La Liga on Saturday and in the Copa del Rey final next Wednesday.
Jos? Mourinho's side have kept eight clean sheets in ten European outings this season, and they succeeded in frustrating Tottenham on Wednesday night.
Crucial games: Real Madrid face Barcelona four times in 18 days
'I expected that Spurs in the first 15 to 20 minutes would come out very determined, but it was not so bad for us,' explained Ronaldo. 'We expected pressure, but they didn't (create) it - we kept the ball.'
Former Liverpool midfielder Xabi Alonso added: 'It was more or less the game that we were expecting. They were going to start really hard and get the crowd behind them; we knew we had to control them and calm the pace of the game.
'It was an intense first half. They did really well, but we've had good control in defence and haven't been conceding goals. In the second half, we knew we would have chances and, as soon as Cristiano scored the goal, it was job done.'
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Explore more:People: Alex Ferguson, Cristiano Ronaldo, Xabi Alonso, Jose Mourinho Places: Madrid, Liverpool, Manchester, Barcelona