The Portugese star temporarily lost the vision in both his eyes after receiving an elbow in the face during Real Madrid's clash with Levante last night.
The £80m man was due to have tests at a Madrid hospital after being caught by a defender.
He had gamely returned to the field and even managed to score Real's opener in the 21st minute but was unable to play the second half after his sight failed.
Coach Jose Mourinho said that his ex-Manchester United ace 'couldn't go on'.
A battered-looking Ronaldo arrived at the Portugal team hotel in Lisbon today but he has been forced to drop out of Portugal's midweek international against Gabon in Libreville.
He was wearing a leather jacket and blue Nike cap but - presumably for the cameras - chose to hook his sunglasses into his T-shirt.
'It was a difficult match for everyone,' Mourinho told a news conference after the 2-1 away win. 'We adapted to the conditions and it was an honest battle between serious people who gave everything in search of a result,' he added.
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