Madrid suffered a 2-1 defeat at the Allianz Arena last week with Mario Gomez netting a late winner for Bayern after Mesut Ozil had cancelled out Franck Ribery's opener for the hosts.
Ozil's away goal means that Madrid will progress through with a 1-0 win at the Bernabeu on Wednesday night, but Ronaldo knows it may not be easy keeping Bayern's strikeforce quiet.
Asked which Bayern player worries him most, Ronaldo told the Bwin.com website: "The players who play up front concern us most. Gomez is one of the leading goalscorers in the Champions League, and Ribery and (Arjen) Robben are also very dangerous.
"They are very good up front, and at the back as well, but we have to be focused on the four in attack because it is one of them who will make the difference."
Nevertheless, the Portugal international is confident it will be his side progressing through to next month's final in Munich as Madrid seek a record 10th European Cup crown.
"We are well. I'm sure that at home we are going to win because we are playing in our stadium, in front of our own fans and we have everything we need to be able to win," he added.
"It's going to be a very difficult game, but I'm hopeful of a Madrid win. They played at home and won, but we got a goal there, which is also important.
"We know that Bayern, after the first leg, are to going to play on the counter-attack, but we also believe that they are going to have a lot of respect for us because we are playing at home.
"I hope we reach the final because it is very important to us players, to Real Madrid and to our fans throughout the world."
The world's most expensive player is hoping his side's supporters will play their part at the Bernabeu on Wednesday, adding: "The crowd has to play the most important role as soon as we step onto the pitch because we can feel it.
"If we stand united, things will turn out well. It is a decisive match and the players are more confident and feel we can do even better when we feel the backing of our supporters."