World Cup 2015: Tyler Morgan & James Hook in Wales centre frame

Wales backs James Hook and Tyler Morgan are vying to start against South Africa

Tyler Morgan and James Hook are both in contention to play outside centre in Saturday's World Cup quarter-final against South Africa at Twickenham, Wales backs coach Rob Howley says.

Injuries to Scott Williams, Cory Allen and Jonathan Davies have left Wales short of options in midfield.

"Tyler was originally picked in our side as a 13," Howley said.

"Over the last couple of games, James has been making sure he's been doing his homework at 12 and 13."

George North was switched to outside centre for the 15-6 Pool A loss to Australia that saw the Wallabies top the table and book a quarter-final against Scotland.

But the British and Irish Lion will revert to his more usual wing role against South Africa following the injury to Liam Williams.

George North started at centre against Australia but is expected to return to the wing against South Africa

Newport Gwent Dragons youngster Morgan and experienced Gloucester utility back Hook are injury call-ups, after missing out on the original 31-man squad for the World Cup.

Hook, 30, has won 80 caps for Wales, while 20-year-old Morgan has won just two caps.

Howley says an injury prevented Morgan from facing the Wallabies at centre.

"We've said about James over the last two years we want to keep James as a number 10, but what's happened over the last five weeks has slightly changed that," Howley said.

"Tyler played really well against Fiji up against an experienced centre as well [Niki Goneva], very physical, and that's probably something we'll defend against and attack against at the weekend as well.

"Putting players in that young, he came through that game really well and maybe if it wasn't for his injury he might have started against Australia."

Howley is expecting that whoever wins selection will need to be aware when South Africa put boot to ball.

"I think it'll be a different game on the weekend, I think it'll be a huge kicking game," he said.

"I think it'll be an aerial battle and there will not be many opportunities."

But Howley is keen to quash any suggestion that Wales might be satisfied with a quarter-final place given their injuries.

"What happened to us back in 2011 in the semi-final of the Rugby World Cup [when Wales lost by a point to France], we want to better that and get to a Rugby World Cup final," he said.

"The attitude of our players has been exemplary, fantastic - we've got a huge task this Saturday and you don't look beyond that."