Both withdrawals are precautionary, though it is not the first time Biggar has had issues with his back. Sam Costelow (22) comes into the matchday 23 to start at fly half.

Williams has a hamstring niggle and is replaced in the starting XV by debutant Cai Evans (24). Tom Rogers (24) takes the place of the latter on the bench.

"They are not serious at all," Wales coach Warren Gatland told reporters. "They could both play on Saturday but the decision was made there's no point in us taking the risk at this stage.

"I see it as a positive. It's dealing with things that are going to be thrown at you. We’ve got four 10s (in the squad). If this was a World Cup semi-final Dan Biggar would have been fine. We’re just taking the precaution. There is no need for us to take a risk with him and it gives Sam another opportunity."

Gatland will name his World Cup squad on Monday and says the game against the Springboks is another chance for players to stake a claim.

"I think we’re getting a bit closer (to knowing his final 33) but there’s an opportunity for players on Saturday," he said. "We’ll head back here as a coaching group on Saturday and finalise the squad.

"We’re confident that those carrying injuries will be available for the first game (of the World Cup) against Fiji."

Gatland also confirmed that Taine Basham (23), who was poleaxed by the shoulder of England fly half Owen Farrell (31) in the 19-17 defeat at Twickenham last Saturday, is also fine after head injury assessment protocols this week. He has been named on the bench.

"He’s had a full week with us from Monday, passed his HIA two and three. No problem at all. He felt fine after the game and when he was on the field."

Asked about the fact that Farrell had escaped a ban after having his red card rescinded by an independent Judicial Commission, a decision that is being appealed by World Rugby, Gatland had little to say.

"I've got no comment on that. That’s last week and we’re focusing on ourselves."