Ronaldo has been left out of the Real Madrid squad to play Real Sociedad on Sunday after failing to make a full recovery from an ankle injury.
Midfielder David Beckham is also doubtful for the game because of a recurrence of his back problems.
Brazil striker Ronaldo aggravated ligament damage in his left ankle after rushing back in order to play in last week's clash against Barcelona which Real lost 3-0. He missed Wednesday's Champions League draw against Olympique Lyon.
Beckham was included in the squad despite being unable to train because of back pain and the club said he will remain a doubt up until the last minute.
The England captain had a fine first half in Real's 1-1 draw against Lyon, but struggled in the second and hobbled off the pitch when he was substituted 10 minutes from time.
"Beckham will travel with us," said Real coach Vanderlei Luxemburgo. "He has undergone treatment instead of training, but we'll have to wait and see if he can play."
Real are also missing captain Raul, England defender Jonathan Woodgate and Danish midfielder Thomas Gravesen through injury.
Real are fourth in the Primera Liga, four points behind leaders Barcelona, while Sociedad are five points further back in 10th.