David Pocock was concussed in the Super Rugby match against the Rebels at the weekend. Photo: David Moir/EPA

SYDNEY – Star flanker David Pocock has failed to recover from a head knock and was Thursday ruled out of the ACT Brumbies Super Rugby clash with the Waikato Chiefs.

No chances are being taken over the health of the key Wallaby in a World Cup year after he was forced from the field after just five minutes in the Brumbies opening-round defeat to the Melbourne Rebels.

He failed a head injury assessment at the time and coach Dan McKellar said his return needed to be carefully managed after a third concussion in less than 12 months.

“We are just following medical protocols there and making sure we do what's best for him,” McKellar told reporters ahead of Saturday's match in Canberra. 

“It's an important year for him and all going well he'll be available for the (round three) Hurricanes game.

“Poey is obviously a massive loss,” he added.

Toni Pulu (eye socket) and Henry Speight (hip) were also ruled out with injury.

Tom Cusack replaces Pocock in the backrow with wingers Andy Muirhead and Chance Peni in for Pulu and Speight.

McKellar has stuck with James Slipper, who served a two-month drug ban last year, as his loose-head prop ahead of Wallabies number one Scott Sio, who will come off the bench.

Agence France-Presse (AFP)