Ronaldo is playing with injury problems, and have done for quite some time. In adition to this he is playing in a quite poor Portugal team. He could still make a difference to help them get through the group, but after that it will be exit for sure. I would not expect anyone to carry this poor squad to anything significant, so its kind of pointless for Ronaldo to waste his health here. But i understand he has desire to always play and win, but he is just stubborn now. His doctor advised him to take a 2 months full rest, but no chance of that in a world cup year.
I really expected Portugal to be stronger than this, they had a good tournament in 2012, but it seems they have dropped in quality a great deal.