Real are joint top of La Liga with Barcelona on 24 points from 10 games but they have looked subdued up front in several matches and there were whistles from the crowd during the 1-0 win over Paris St Germain in the Champions League on Tuesday.
Benitez has pointed to injuries to key players and clearly any side would miss Gareth Bale and Karim Benzema, who were sidelined against PSG, while James Rodriguez was only fit for a place on the bench.
In previous seasons Real have been able to call on Ronaldo to lead from the front, in a similar style to Lionel Messi at Barcelona, but the Portuguese has fallen below his high standards this term.
He has been widely criticised in particular for his performance against PSG.
"Cristiano had his worst match in memory," said respected Spanish journalist Alfredo Relano in the As newspaper.
"There are two major problems at the moment, the injury crisis and the alarming drop in form of Cristiano."
As part of the remodelling of the side under Benitez this season, Ronaldo has featured as a traditional number nine rather than in his preferred position as a striker drifting in from the left.
Figures from football statisticians Opta show that against PSG, none of the former Manchester United forward's 46 touches of the ball came inside the penalty area.
Ronaldo has a good return of 13 goals from 14 games this season but that is largely down to the five he scored against Espanyol. At the same stage last season he had notched 20 goals.
Real face Europa League champions Sevilla who are 11th in the table but showed their potential with a victory over Barcelona a month ago.
"We need to keep going to achieve our aims in the league," Sevilla coach Unai Emery told reporters after their home defeat in the Champions League by Manchester City on Tuesday.
"It will be a great game against Real and there is always a special atmosphere when we play them. We have had new players coming in this season and it takes time for them to settle."
Barca take on Villarreal on Sunday looking for their fourth straight win in La Liga and have their own injury problems with Ivan Rakitic joining Messi and Rafinha on the sidelines.
(Editing by Tony Jimenez)
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