Wallabies bolter Brett Sheehan is hoping a freakish training mishap will not rule him out of the most important match of his life.

Sheehan suffered a suspected fractured eye socket when struck by the corner of a tackle bag in a drill with Wallabies skills coach Scott Wisemantel at the very end of a training session in Canberra on Thursday.

Late on Thursday, the 26-year-old NSW Waratah was being taken to hospital to see an opthamologist.

Amid concerns teenage star Josh Holmes was too risky a proposition, Sheehan had emerged as the frontrunner to be George Gregan's back-up halfback for Australia's must-win Tri Nations Test against New Zealand on Saturday week.

A distressed Sheehan was temporarily blinded in the right eye when the accident first happened.

Asked if the injury was serious, Sheehan said: "I hope not. That'd be good, wouldn't it."

Sheehan's injury scare was the last thing the Wallabies needed with fellow halfbacks Sam Cordingley (foot) and Josh Valentine (ankle) already ruled out.

Cordingley had been mounting a serious challenge to Gregan's No.9 position before suffering a recurrence of a foot injury that sidelined him for most of the Super 14 season in Australia's unconvincing win over South Africa in Sydney last Saturday night.

He said he would be back on crutches next week and out for at least a month.

In a best-case scenario, Cordingley will be available for the Wallabies' end-of-season tour of Europe but he admitted he may require surgery and another long stint on the sideline.

Like Cordingley, Valentine will also miss the rest of the Tri Nations tournament, leaving Sheehan and Holmes in a two-way race to win the role as Gregan's deputy.

While Wallabies coach John Connolly insisted he remained undecided about which to pick - and that he was even considering a third and much less likely scenario of using Matt Giteau as reserve scrumhalf - five-eighth Stephen Larkham felt it was probably too soon to thrust Holmes into the Test arena.

Holmes, the Australian under-21s captain, is widely considered to be Gregan's long-term successor but Larkham echoed Connolly's and assistant coach Scott Johnson's concerns of earlier in the week that the 19-year-old might not be ready to face the might of the All Blacks.

Unlike Sheehan, who has two years' experience at provincial level, Holmes has yet to even play Super 14 football.

"The step up from Super 14 to Test level is quite a big step and, to not even have played Super 14 level, it's going to be a big ask to try and step up and play Test level," Larkham said.

Regardless of who gets the nod, Larkham maintains Gregan, despite being under constant pressure to retain his job, remains Australia's premier halfback and captain 10 months out from the World Cup in France.

"I think George has been playing extremely well this year and he's come under a bit of harsh criticism, particularly after the South African game, which the whole side was pretty flat going into," he said.

"I've got a very good understanding with George. I've played with him for over 10 years now and I've always said I wouldn't have any other halfback inside me and I think that still holds true today.

"George is playing some of the best football of his career.

"All the players in the side are very happy with the way George is playing and very happy with him to be captain because he certainly leads by example.

"He takes a lot of pressure off some of the younger players in the team because the experience he brings."

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