Angola's star striker Mantorras has been ruled out for almost the entire season after a knee operation in Lisbon on Monday.

The Benfica player aggravated a cartilage during training last week on his right knee.

The knee had previously ungone surgery last February.

His collision with team mate Ricardo Rocha was initially thought to be mild, but doctors say he will be out of action between three to six months.

This could mean he will not be fully fit until the end of the Portuguese league.

Mantorras said he was saddened by the event of a second operation, but he remains optimistic of returning to action and will not let the injury blow frustrate him.

Although the 22-year-old may be discharged from hospital today, Benfica doctor Bernardo Vasconcelos said a long period of recuperation is required.

Mantorras's career since he moved from Alverca to Benfica last year has been plagued by the knee injury, which has affected his form and rating as one of the finest to have played in the Stadium of Light since the legendary Eusebio.