Ronaldo has not featured since April 20, but could return for the second leg having missed last week's 0-0 draw at the Etihad Stadium.
"Every Champions League match feels like the first," Ronaldo told the club's website. "And Real Madrid's priority is to win.
"We know it will be a tough challenge, but everything is possible."
The 31-year-old Portuguese trained with his team mates during the first half of Sunday's session before working out on the pitch alone.
"Manchester City are in the semi-finals because they are an excellent team," Ronaldo added.
"Eliminating Paris St Germain is not easy, but they managed it. They're a team who have very few flaws."
Striker Karim Benzema also continued his recovery from a hamstring injury and Alvaro Arbeloa - who has not played since early April - completed some running exercises.
Ronaldo leads the Champions League scoring charts with 16 goals this season, including a hat-trick in the quarter-final second-leg victory over Wolfsburg.
"We had to win by three goals and I scored all three," Ronaldo said.
"It was a special night. It needed to be the perfect evening and it was."
(Reporting by Ed Dove, editing by Ed Osmond)
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