But Ronaldo was upbeat about Madrid's chances of repeating last term's 2-1 success in Catalonia, which virtually assured the title for the capital club.
"We know what it is going to be like against Barcelona, but we've won there," the Portuguese star said on Television Espanola.
"It will be a tough game. It's important to us and we have to concentrate and be confident in producing a good game.
"I think we are going to win. We have the quality to win at the Camp Nou. We will see what happens."
Riki gave the visitors a shock lead on 15 minutes at the Bernabeu but Real was level seven minutes later when Ronaldo scored from the penalty spot after
And the host was in cruise control by half-time as
Pepe headed in the fourth 25 minutes from time following Xabi Alonso's free-kick, before Ronaldo completed his treble with another penalty after Evaldo had been harshly adjudged to have handled Kaka's cross.
Ronaldo acknowledged the importance of the victory given his side's surprisingly poor start to the defence of its title, which has included defeats to Getafe and Sevilla and a home draw against Valencia.
"We were a bit asleep at the beginning but then woke up and played a good game," the 27-year-old said.
"We knew we could not afford to lose any more points and it was a very important victory."
"It was a league match. It's three points and we will analyse it tomorrow (Monday Spanish time), as with every match, and draw the necessary conclusions - especially taking into account Wednesday's match, which is the next thing to tackle," he said.
"We have the feeling that we need to concentrate on ourselves - to keep improving and growing and win the league matches that we have.
"We are thinking about Wednesday's match and afterwards we will think about the Barcelona match."
Real Madrid coach Jose Mourinho remained non-committal about where he will be next term after his side lost 2-1 in the Copa del Rey final against local rival Atletico Madrid to round off the "worst season" of his life.