Reds coach and former Wallabies prop Ewen McKenzie believes the time is right to inject the super-sized sub.

McKenzie would like to see SANZAR adopt the European model of eight-man benches in Super Rugby, adding an extra prop to guard against matches going to uncontested scrums due to front-row injuries.

A blight on the code, non-push scrums are in the spotlight after the NSW Waratahs were controversially forced into de-powered contests in last weekend's loss to the Bulls after losing props Benn Robinson (ankle) and Paddy Ryan (neck) to injury.

Some South African critics were suspicious the Waratahs may have pulled a swifty to avoid packing energy-sapping scrums against their huge forward pack at altitude in Pretoria.

But McKenzie felt SANZAR should follow the example of French rugby in cleaning up the problem by having one more replacement front-rower on the bench, lifting game-day squads from 22 to 23.

"I enjoyed coaching in France where they have 23-man squads with an extra prop," said the 51-Test former tight-head who coached Stade Francais for two seasons.

"They had a lot of uncontested scrum situations happening and then they changed it and it tidied it up very quickly.

"It's a model that works well in Europe and it will be interesting if they look at it from a SANZAR point of view."

McKenzie said the benefits of a having one more reserve prop included extra safety as well as ensuring less collapsed scrums through improved development of rising front-rowers.

"It was a great tool to be able to expose and develop, particularly young props, as you can have that 23rd player as a young prop and you can be introducing them into the game so they get experience, otherwise they go in cold at some point," he said.

"I know from a coaching point of view the upside was you could play a specialist loose-head and tight-head on the bench and you could play them in their specialist position rather than a hybrid - a guy who goes out there and covers both who might not be as technically good on the other side.

"That way you actually get some prop development."

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