Van Niekerk's opening try against Samoa (Getty Images)

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South Africa's World Cup campaign suffered a major setback when flanker Joe van Niekerk was ruled out of the tournament.

Van Niekerk could be sidelined for six months after tearing the anterior cruciate ligament in his right knee during yesterday's 60-10 victory over Samoa in Brisbane that clinched a quarter-final place.

South Africa's player of the year in 2002 will now be flown home to consult a specialist and probably face surgery.

South Africa have yet to decide on a possible replacement, but the loss of van Niekerk will hit them hard as they prepare for next weekend's quarter-final.

Lock Victor Matfield (ankle) and prop Christo Bezuidenhout (knee) also picked up injuries during the Samoan match but they are expected to be fit in time.

And with the Springboks pack rapidly developing into a fearsome unit, coach Rudolf Straeuli can only hope that his quarter-final plans are not further disrupted following the loss of van Niekerk.

"If we can keep this pack together, and with the other opportunities coming from the bench, we have got depth coming from the forwards," said Straeuli in the aftermath of a game that saw South Africa score eight tries and their exciting fly-half prospect Derick Hougaard amass 21 points.

"We are just taking it game by game. We are confident within ourselves that we have the ability.

"We have had a hard year on and off the field. We have improved day by day in terms of fitness, team spirit and unity, and I am proud to be coaching a team like this."

Straeuli though, believes there is an issue surrounding technical infringements, and a Springboks' perception that they are being punished more than other teams.

"We get warned a lot, but technical infringements of other teams don't get picked up," he added. "We are writing reports on that, and going through the right channels."

Straeuli could feel highly satisfied with the Springboks' eight-try demolition of Samoa, which was built on a platform of raw forward power.

South Africa never looked back once van Niekerk crossed for a second-minute try, and further touchdowns followed at regular intervals from Hougaard, Jorrie Muller, Juan Smith, Ashwin Willemse, Jaque Fourie, Jaco van der Westhuyzen and Neil de Kock.

"I think we are a little bit better equipped now," said Springboks skipper Corne Krige.

"We went through a tough physical and mental campaign this year, and nothing that the All Blacks or Australia throws at us now can be worse than what we have already been through."

Hougaard must retain his place for the quarter-final on Saturday's evidence, when he controlled matters behind a dominant South Africa eight.

He mixed his running and kicking game with the expertise of a seasoned international performer, although his lasting memory would have been a crunching tackle on him by Samoan centre Brian 'The Chiropractor' Lima.

Hougaard was pole-axed by the totally legal tackle, but he could at least see the funny side.

"That was the hardest tackle I have taken in my life," he said. "But I am still breathing, so that is a good sign."