Skinstad's absence would be a big loss to South Africa

The injury was sustained during a club match on Saturday and will leave Skinstad on the sidelines for at least a month.

"Bob is expected to wear a cast for between four and six weeks," Skinstad's agent Craig Livingstone confirmed.

The 27-year-old has missed most of the international season through injury.

On his last Springbok appearance he came off the bench in a 26-25 victory over Argentina in June.

He was included in the South Africa squad for the home leg of the Tri-Nations series but did not play and was then left out of the 28-man squad for the games in Australia and New Zealand.

Skinstad, who is currently not contracted to a provincial union, was told by national coach Rudolf Straeuli to get game time in club rugby to prove his fitness ahead of the World Cup.

But the number eight, who has won 34 caps for his country, is now likely to miss the October showpiece unless Straeuli gambles on including him in a 30-man squad at the end of the month.