NSW Waratahs fullback Sam Norton-Knight has been ruled out of Saturday morning's must-win Super 14 clash with the Cheetahs with a back injury.

Norton-Knight was named on the bench for the round twelve encounter, however was unable to complete the Captain's Run at Grey College in Bloemfontein after suffering a back spasm.

Randwick centre Matt Carraro has been called into the squad to replace Norton-Knight.

"It's a shame for Sam for this to happen so close to the game, especially on the back of copping a knock on his ankle just before heading to South Africa," said Waratahs coach Chris Hickey.

"It gives Matt an opportunity from the bench this week and he performed extremely well when he was in South Africa last year so I'm sure he will do the job extremely well."

The squad completed their Captain's Run at Grey College, before familiarising themselves with Vodacom Park.

"The kickers had a good chance to get their bearings in the stadium, which is pretty important," Hickey said.

"There's also a lot of renovations going on for the Soccer World Cup at the ground, so getting a look at the new facilities was good."

The clash with the Cheetahs kicks off at 1.05am (AEST) on Saturday.

NSW Waratahs: Lachie Turner, Peter Playford, Timana Tahu, Kurtley Beale, Lote Tuqiri, Daniel Halangahu, Brett Sheehan, Wycliff Palu, Phil Waugh (capt), Ben Mowen, Will Caldwell, Dean Mumm, Al Baxter, Tatafu Polota-Nau, Benn Robinson. Res: Damien Fitzpatrick, Sekope Kepu, Chris Thomson, Luke Doherty, Luke Burgess, Matt Carraro, Tom Carter.

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