Barcelona's Thiago Motta looks set to miss next week's UEFA Champions League clash with Benfica.
The Brazilian ace sustained a leg injury in Saturday's 1-1 draw with Real Madrid at Camp Nou.
Motta was forced to pull up quickly after trying to chase back to catch Ronaldo as he scored the equaliser for Real.
The versatile performer is set to undergo scans on the problem on Sunday, but it is likely he faces a lengthy spell on the sidelines.
Meanwhile, Ronaldo has hit at referee Luis Medina Cantalejo following his performance in Saturday's clash with Barcelona.
Cantalejo sent off Roberto Carlos in the first half and Ronaldo insists his team-mate did nothing to deserve the red card.
"Roberto told me he had done nothing to offend the referee," said Ronaldo. "He's a phenomenon if he heard an insult given the noise out there in the stadium.
"The referees seem to be against us. They blow for non-existent penalties and free kicks."