James O'Connor's rapid improvement in defence has come at a cost, with a litany of heavy hits ruling the star Western Force back out of Friday's Super Rugby clash with the Hurricanes in New Zealand.

The Force will field a severely-depleted backline against the Hurricanes after O'Connor, five-eighth Willie Ripia, centre Gene Fairbanks and scrumhalf Brett Sheehan were ruled out through injury.

O'Connor, who saw a specialist earlier this week and would remain in Perth to receive treatment on his shoulders and neck, was considered a certainty to return for the Force's match against the Highlanders in Dunedin on June 3.

The Wallabies star has long been renowned for his dazzling footwork and accurate goalkicking.

But the 20-year-old has also improved his tackling significantly this season, with his unrelenting approach resulting in more hits to his upper body.

"There's no neck damage as such, but he just keeps getting knocks in that upper body region," coach Richard Graham told AAP on Wednesday.

"If you have a look at him this year, I think probably the area of his game that has improved the most has been his defence.

"His defence in that frontline has been absolutely fantastic.

"Pound for pound, he's one of the strongest in the game, probably he and (Will) Genia together.

"We've taken him out of the frontline at times and played him at fullback just to give him a spell so he doesn't have to make so many tackles.

"We've just been easing him through the weeks to get him up for games.

"At some time, I knew I was going to have to make a decision to give him the week off and do some work on him physically, and that's come this week."

In the absence of Ripia, back-up scrumhalf James Stannard will fill in at No.10, while 20-year-old rookie Mark Swanepoel has been given the nod at scrumhalf.

Fullback Cameron Shepherd will take on the kicking duties after recovering from minor knee surgery.

Graham said the torrid conditions expected for Friday's match could help protect his depleted backline.

"We expect the forecast to be miserable, so it's going to be a game where the forwards are going to be asked to do a lot of the work," Graham said.

"You can't ask the forward pack to do everything, so there has to be that balance. But the conditions are going to be very much forward-oriented.

"At three o'clock this morning, I thought someone was throwing stones at my window. It was actually the wind pushing the rain against the hotel window."

Graham backed Stannard and Swanepoel to lift for the occasion.

Force: Cameron Shepherd, Nick Cummins, Patrick Dellit, Rory Sidey, David Smith, James Stannard, Mark Swanepoel, Ben McCalman, David Pocock, Matt Hodgson, Nathan Sharpe (capt), Sam Wykes, Tim Fairbrother, Nathan Charles, Kieran Longbottom. Res: Ben Whittaker, Matt Dunning, Tom Hockings, Richard Brown, Chris Cottee, Mitch Inman, Alfie Mafi.

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