The Seleccao still have a chance of making the last 16. But even if they were to beat Ghana in their final match, a draw between Germany and the United States would see those two sides advance from Group G.
Paulo Bento's men were without four players through injury or suspension for Sunday's 2-2 draw with the US, and Ronaldo says the squad is not good enough to cope.
PHOTOS: Beautiful people in Brazil | Brazil protests | Soccer fanatics | Fan tattoos
"Maybe we're an average team," he said. "It would be a lie to say that we are a 'top' team. We have many limitations and suffer from injuries such as with Pepe [who was suspended] and [Fabio] Coentrao. This limits us a lot. We have a very limited team and we are not at the best level. This does not enable you to beat top teams.
"There are no miracles. We knew we would have a tough group, with perhaps teams better than us. I never thought we could be world champions, we have to be humble and know our level. I'm not a hypocrite, I never thought we could win the tournament "
The 29-year-old was not as candid about the knee injury which has troubled him since the end of the domestic season, but did hint at the extent of the problem and insisted he would battle on.
"I don't want to justify myself by talking about my physical problems, that's water under the bridge," he added. "I'm here, I'm fighting, I'm trying to do my best, I'm running, and obviously it's no use talking about my issues.
"Every day there's something new in the papers about my knee, and about this and that. That's why I don't want to justify myself. I'm here body and soul to help the national team."
Ronaldo also acknowledged that Portugal looked tired against Jurgen Klinsmann's men in the humid conditions of the Amazon, but did not feel able to expand on that topic because of his own struggles.
"I'm not the most adequate person to answer that question, especially because I don't have the moral high ground here since I haven't been playing the way I would hope lately," Ronaldo said. "Obviously we had a very long season, but every team here did as well. They were also playing the Champions League and cups and leagues, so it's something everyone else could point out as well.
"I don't think we lost the game because our players lacked attitude. Every team comes here to win. We knew we weren't favorites, we have never been."