Real Madrid goalkeeper and captain Iker Casillas fractured the thumb in his left hand during Wednesday's King's Cup quarter-final second leg in Valencia, the Spanish club said Thursday.
The 31-year-old was forced off the pitch 16 minutes into the contest after team mate Alvaro Arbeloa accidentally kicked his hand as he attempted a clearance.
"After carrying out initial x-rays at the La Moraleja Sanitas Hospital it has been confirmed that the footballer Iker Casillas has suffered a fracture at the base of the first metacarpal on his left hand," the club said in a statement.
"It will be assessed again by a specialist later today to decide what treatment will be followed."
Real Madrid gave no estimate for how long Casillas may be sidelined but Spanish media reported that an injury of this type could take up to three months to heal.
He was replaced during Wednesday's match by reserve keeper Antonio Adan and Real Madrid went on to secure a 1-1 draw that put them into the semi-finals 3-1 on aggregate.
Real Madrid face Getafe in the Spanish league on Sunday and will confront Manchester United at home in the first leg of the Champions League last 16.