The Brazilian striker, the joint top scorer in La Liga this season, is out for a month after picking up an ankle injury on Saturday.
Real Madrid have won more than 63 per cent of their games when Ronaldo has featured in the line-up. Without him, the figure drops to just 41 per cent.
Ronaldo was suspended for the opening games against Lyon and Olympiakos. The team lost 3-0 in France and edged the Greek side 2-1 at home. The nine-times European champions lie third in Group F with three points, behind Rosenborg on goal difference. Lyon are top with six points while Olympiakos are last with none.
"It's the most important match so far this season," the Madrid coach Wanderley Luxemburgo said. "If we don't win, we'll have difficulties qualifying. We have to be very concentrated and play as if it was a final."
Madrid's European worries contrast with their strong domestic form. Luxemburgo's team beat city rival's Atletico 3-0 on Saturday to top La Liga for the first time in 18 months. Ronaldo scored twice to take his season's total to seven.
"I think we can play even better, but from the beginning of the season up to now we have needed time," the French midfielder Zinedine Zidane said. "The team had to be given time to settle."
The Madrid captain Raul, who scored his 50th goal against Olympiakos to become the all-time leading scorer in Europe's top club competition, will make his 100th Champions' League appearance tonight.
With right-back Michel Salgado injured and central defender Sergio Ramos suspended, Madrid will need to rearrange their defence. Jonathan Woodgate is expected to make his European debut for Madrid.
The England defender has scored two own goals since returning from a 17-month injury layoff. "If he ends as our top scorer we'll have a problem," Luxemburgo joked. "I've got a lot of confidence in him."
Rosenborg, who have won 13 consecutive Norwegian league titles and qualified for the Champions' League nine times in the past 10 years, have endured a poor domestic season this time.
However, the Trondheim team were boosted by Sunday's 4-1 win over Brann Bergen, which all but ensured that they will avoid relegation.
"We have scored 13 goals in three games and it shows we're in top form," said the Rosenborg coach Per-Mathias Hogmo, who insisted that the Norwegians had a chance of beating Madrid.
"It will be fun. I have a good feeling about it. It will be a match between two teams who are on form," Hogmo said.
The Rosenborg goalkeeper Espen Johnsen, who missed Sunday's game, has recovered from a knee injury and should play.
* The Deportivo La Coruña defender Jorge Andrade will be out for up to a month with a thigh injury. The Portugal international was hurt during Deportivo's 3-3 draw with Barcelona on Saturday, and is expected to miss league games against Real Sociedad, Real Madrid, Getafe and Malaga.
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