The Portuguese forward was untroubled by the ankle injury that had kept him on the sidelines for the last two months when he came on for the last 20 minutes of Real's drab 1-0 Champions League win over FC Zurich on Wednesday.
"I'll definitely be able to play against Barca. I feel good, I want to play, and it is up to the coach whether I go from the start," Ronaldo told reporters.
Real took first place from Barca in La Liga last weekend and have a one-point advantage over the champions, but as ever the 'clasico' is much more than just a top-of-the-table tussle.
It is about a clash of styles, and a chance to see how the new-look Real measure up against their arch-rivals, the treble-winners.
The return of Florentino Perez to the Real presidency has seen them invest around 250 million euros in players such as Ronaldo, Kaka and Karim Benzema.
However, under new coach Manuel Pellegrini they are struggling to gel as a unit and to provide the spectacle demanded by the fans. The team have lacked personality and bite in Ronaldo's absence.
"It's likely they (the squad) are suffering from excessive anxiety, pressure, criticism, and some aspects of the game are not working well," Pellegrini said after the visit of Zurich.
"Because of this the team deserve a lot of credit to be where they are now. We aren't playing badly, we just aren't entertaining."
TEAM ETHIC
Barcelona are still winning plaudits for their eye-catching football, played with a squad of largely homegrown talent and built around a strong team ethic.
Tuesday's impressive 2-0 Champions League win over Inter Milan was achieved without two of their biggest names, Zlatan Ibrahimovic and Lionel Messi, who were on the bench nursing thigh injuries.
They were barely missed as Barca ended an indifferent run of form in which they drew three of their previous five matches in all competitions.
"If we look at the stats, Barca don't score more goals than us and don't concede fewer, and we have more points," Pellegrini added. "I admit the style of play is different. They have a well-defined concept and we are in search of something different to previous years."
Ibrahimovic and Messi look set to recover in time to help unbeaten Barca defend their 100 percent record at home in the league.
Real have lost only once so far, away to Sevilla last month, but have nine wins from 11 and will be keen to erase the memory of their last meeting with Barca in May, when they were humiliated 6-2 at the Bernabeu.
"We need to be prudent and respectful because they are the leaders," defender Gerard Pique told Barca TV.
Third-placed Sevilla visit basement side Malaga on Saturday, and fourth-placed Valencia host Real Mallorca, who are sixth.
