Brazil striker Ronaldo injured his calf muscle in training on Thursday and is ruled out of Real Madrid's King's Cup match against Athletic Bilbao, the club's website said.
Ronaldo will miss the Jan. 3 game at Bilbao in the last 16 of the Cup and a friendly against Atletico Madrid on Friday.
Real were already without striker and captain Raul who suffered a serious knee injury in November.
They have slipped to fifth in the Primera Liga, 11 points behind league leaders and arch-rivals Barcelona.
English defender Jonathan Woodgate, who suffered a hamstring injury in November, returned to full training on Thursday.
