Eli Walker will not feature for Wales in their Rugby World Cup quarter-final against South Africa, despite being called into the squad to replace the injured Liam Williams.

The Ospreys wing was drafted in on Tuesday having been forced to withdraw from Warren Gatland's original 31-man squad with a hamstring problem.

Walker has now overcome that injury but is not ready to be thrown into the mix for Saturday's clash with the Springboks - George North and Alex Cuthbert expected to line up on the wings.

"He's not available for selection this weekend," said backs coach Rob Howley. "He's just got over his injury. He'd be available for a semi-final.

"If you look at the South African strengths, it's an aerial battle. George and Alex will be on the wings to negate that threat of Bryan Habana and JP Pietersen."

Wales will be boosted by the news that centre Jamie Roberts is in contention after taking a blow to the head in a bruising 15-6 defeat to Australia last weekend.

Howley added: "Jamie Roberts is fine. He's been through the concussion protocols and is available for selection."

Wales triumphed 12-6 over South Africa in Cardiff last year and ran the Springboks close in a 31-30 defeat when the sides met in Nelspruit earlier in 2014.

"When you beat a side it gives you confidence... [but] that side they played against us was outside the international window," Howley explained.

"They have been refocused since [losing their opener to] Japan. It is always attritional against South Africa. They are one of the most experienced line-ups in Rugby World Cup.

"We have come through tough games against tier-one nations and that gives us a good platform and prepares us for what will come on Saturday against South Africa.

"International rugby is about taking chances. We were composed against England but we came up short against Australia and it could have been better.

"As long as you learn from that, that's the main thing."