HIS elevation has been swift and dramatic. Berrick Barnes has gone from being the last squad member picked to the most important Wallaby, following news that Stephen Larkham might miss the rest of the tournament.

While Wallabies officials hope Larkham will overcome his knee problems in time for the World Cup semi-final, they concede the chances are not good. Instead, the Wallabies are expecting the novice Barnes to be their Test five-eighth for the remaining matches in France.

Larkham began walking on Wednesday as part of his rehabilitation following his second knee operation, and was adamant he would be fit in time for the semi-final.

He planned to spend an extra day in hospital, hoping to join the rest of the Wallabies when they depart for Bordeaux on Thursday for Saturday's final pool match against Canada.

Speaking from his hospital bed, Larkham told the Herald that while deeply disappointed about having to undergo a second operation after suffering an infection from the initial arthroscopy, he did not believe his Test career was over.

"I do feel a lot better than yesterday, and the swelling has come down a bit," Larkham said. "I will do some walking every two hours, and we are hoping that I will get out of hospital tomorrow."

Larkham admitted he had been a "little bit worried" about his playing future before the second operation.

"Thankfully, the infection was on the outside of the knee, and not within the knee joint. Our team doctor [Martin Raftery] definitely made the right decision of me returning to hospital as soon as possible, and we were able to get at it early enough. So I am feeling lot more happier now."

Larkham agreed with Raftery that it would be around a week before he would know whether he was a possibility of playing again in the tournament.

"I am hoping everything will be cleared out by Monday, and I am certainly hoping of playing again in this World Cup," Larkham said.

When asked if he was targeting the semi-final, Larkham replied: "At this stage, I believe that is realistic."

However, Wallabies officials realise that if Australia are to win the Webb Ellis Cup for a third time, Barnes will need to become the latest Australian sporting superstar.

Already, a David-and-Goliath encounter is anticipated next week if England advance to the quarter-final in Marseille, with Barnes set to oppose the man who won England the 2003 World Cup final - Jonny Wilkinson.

The logical course would be for Australia to immediately call for a replacement for Larkham, and call up the in-form Kurtley Beale to join the squad from Sydney.

Even if Larkham is able to recover in time, there are questions about his lack of match fitness for the knock-out phase, amid concerns he looked well out of sorts in his only appearance so far, against Japan.

Larkham is a confidence player. Having a wonky knee will not help the 33-year-old's state of mind at all, nor will it alleviate the selectors' anxiety over choosing players at the end of their careers for this World Cup.

But such is the hold Larkham has on the Wallabies that management will wait until the last moment before deciding whether he stays or a replacement is required. That decision could come too late to save Australia.

It will be at least a week before officials have any idea whether Larkham will recover quickly enough and how long it will be before he is even able to run. Yet the Wallabies keep saying that he should not be cast off just yet.

"We've got to give him time," assistant coach and selector Scott Johnson said. "You owe it to the team and you owe it to Stephen to give him as much chance as we can. Now that we're through [to the quarter-finals], we've bought ourselves some time.

"It is always discouraging when a player gets some issues he didn't expect. It is his swan song, and he doesn't want to cut it short. So there was all that frustration and disappointment, but he was in good spirits when we visited him in hospital, and he got more encouraging news today."

Dr Raftery said the best scenario was a semi-final return for Larkham.

"He's had an infection between the skin and his knee, not within the knee," he said. "It was then decided he would have surgery, to have his knee drained. The infection was the result of the original surgery.

"The first job is to get that swelling down. If we can get that down pretty quickly, we are going to be on target. If we fail to get that down, or he doesn't respond, then it is going to be slower.

"In a week's time, we'll be able to give a much clearer picture of where we are heading."

Regardless of Larkham's availability, Johnson said he had complete confidence in Barnes's ability.

"Berrick has been a breath of fresh air," Johnson said. "Necessity is the mother of invention, but he has allowed us as a country to be six months ahead of where we are scheduled.

"He's got some quality Test matches under his belt."

In a bid to relieve the pressure on Barnes, he has been rested from the final group match against Canada in Bordeaux on Saturday. Julian Huxley has taken his spot.