Rome - AC Milan goalkeeper Christian Abbiati successfully underwent knee surgery Monday in Belgium and began rehabilitation expected to last six months, his club's website reported.

Abbiati, 31, damaged the cruciate ligament in his right knee clashing with team mate Giuseppe Favalli on March 15 during a Serie A game against Siena.

A similar operation could be necessary for international striker Antonio Di Natale, who was stretchered off the pitch Saturday as Italy beat Montenegro 2-0 in a 2010 World Cup qualifier.

Di Natale, 31, damaged the cruciate ligament in his left knee as he slipped away from the ball on a wet pitch.

The knee was to be examined Tuesday in a Barcelona clinic, where doctors will recommend treating the damaged ligament either with or without surgery. The latter option should only require a 45-day absence.

In each case, Udinese will miss Di Natale for the last nine Serie A games and in the UEFA Cup. If operated, he won't be available for the Confederations Cup featuring world champions Italy in June in South Africa. (dpa)