Brumbies' winger Henry Speight has been ruled out of Saturday night's Super Rugby clash with NSW because of a knee injury.

The 22-year-old Fijian has struggled with his knee since the Canberra-side's home win against the Melbourne Rebels last weekend.

"He's had trouble stepping and accelerating on his knee for a week and that was not good enough," Brumbies coach Tony Rea said on ABC Radio on Saturday.

Rea has promoted Andrew Smith from the bench to replace Speight, while Francis Fainifo moves into the matchday squad for the game at Sydney's Olympic Stadium.

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