Umaga lost his race to recover from ruptured knee ligaments in time for Saturday's World Cup quarterfinal at Docklands when he was omitted from New Zealand's 22-man squad for the game.

But the fact that Umaga even stood a chance of selection following an injury that at one stage looked to have put him out of the tournament has given New Zealand's players an enormous fillip.

Scrumhalf Justin Marshall said Umaga's determination not to be beaten by a potentially tournament-ending injury had inspired other members of the squad, even if there was sadness at his absence on the pitch.

"Tana has been an important cog for the past five or six years now," Marshall said.

"But don't underestimate the value that he gives just by still being here with the team. To see him while we're training, off running by himself and making the effort to get himself fit, you can see what it means to him.

"Other guys see that and they respond — it lifts us."

Umaga is also exerting his influence on a more practical level, offering advice and support to his relatively inexperienced replacement Leon MacDonald. MacDonald is a fullback by trade but has successfully slotted in at centre in Umaga's absence.

"Tana's obviously taken a lot of interest in the way I've been playing," the 25-year-old Canterbury player said.

"He's offered a few tips and I'm grateful for that. I've been working very hard this week on some of the things he's mentioned and that's a great help."

"A lot of it is quite subtle stuff, like technique in the tackle. Tana's a master at winning turnover ball in contact, and hopefully he can pass some of that off on me."

Despite raised hopes earlier this week of Umaga making a comeback against the South Africans, New Zealand coaches John Mitchell and Robbie Deans opted against it after a fitness test on Tuesday.

"He's not quite right. He suffered a little bit of aggravation on Tuesday during a run-out," Mitchell said. "But it's not over for Tana. There's every opportunity he could be available next week."