HAMBURG, Germany -- Vitali Klitschko, who lost his WBO heavyweight title to American Chris Byrd on Saturday, will undergo a shoulder operation for a torn rotator cuff.

Doctors at Hamburg's Fleetklinik, where he was examined, on Tuesday said the surgery gave the Ukrainian the best chance to fight again this year. Klitschko will be sidelined for at least four to six months.

Klitschko, making his third defense of the lightly regarded crown, refused to answer the bell for the 10th round of the scheduled 12-rounder against Byrd, saying later he began to feel fierce pain in the third round.

Klitschko is 27-1, with all his wins coming by knockouts.