Ronaldo is likely to be United's biggest threat on Sunday with the Portuguese ace bringing his season tally to 33 goals, via his brace in the midweek win over Bolton.
"I think they have a lot of good players so if you are just thinking about Ronaldo it will be difficult. We need to think about all of them," said Benitez.
"In these kind of games the small details will be the difference."
Benitez has been impressed by Torres' impact in his debut season and he has backed Sir Alex Ferguson's call for referees to give more protection to attacking players like Ronaldo and Torres.
"I think he's [Ronaldo] in form but Torres is too. The other day Ferguson was talking about referees having to protect Ronaldo," added Benitez.
"I think it's important to protect players like Torres, Ronaldo and all players with quality."