Rooney has failed to impress during the tournament so far, producing lacklustre displays in both the 1-1 draw against the United States and Friday's stalemate with Algeria in Cape Town.
The Manchester United forward has looked sluggish and uninspired in South Africa so far and made matters worse for himself with a snarling comment to a pitch-side television camera about England fans' booing after the Algeria performance.
However, his former United team-mate Ronaldo, whose Portugal side face North Korea tomorrow, was quick to defend his friend.
The Real Madrid forward said: "Wayne Rooney tried very hard, he's always like that, but he didn't play alone. So it's difficult, when it's not coming, when you don't score a goal or play well, it is always the big players' fault. Wayne is a great player and will do a good job. He'll try very hard to do a good job."
Ronaldo, himself suffering a barren spell having not scored competitively since UEFA Euro 2008, added: "I saw England's games and I'm quite surprised they didn't win them."