South African fast bowler Makhaya Ntini has injured his knee and will not bowl again during the second Test against Australia and has been ruled out of the third Test in Sydney, a team spokesman said on Thursday.

The 28-year-old suffered a torn medial ligament in his left knee on Wednesday and underwent a fitness test on Thursday.

A team spokesman said Ntini had been able to run, but felt sharp pain when he attempted to land on his front leg as he bowled.

Andre Nel and Shaun Pollock opened the bowling on day four for the Proteas.

Ntini is expected to be able to bat in South Africa's second innings, if required.

The third and final Test begins on January 2.