Lyon are in Madrid defending a 1-0 lead from the first-leg.
"Wednesday's match is do-or-die," said Ronaldo, the competition's top scorer this season with six goals so far. "We are playing very good football and we have proved that we are the strongest team in La Liga.
"We are familiar with Lyon. They are a strong team physically speaking, but it's our turn to play at home.
"I am convinced that this team will respond and that we will make it through to the next round."