McCaw is still struggling with a foot injury, described as niggly by All Black coach Graham Henry, and there is real doubt whether he can play the All Blacks' three remaining games in the tournament, if they go that far.
Henry said yesterday he could give no assurance that McCaw would be right, saying no more would be known until after he played tomorrow.
"He just runs on it, it feels good, then he wakes up the next day and it is niggly again," he said. "So, hopefully, we have got three games ahead of us and it is about making sure he is available for each of those three games.
"He has just got to do what he can during the week to perform in the weekend. He has been controlling himself very well."
McCaw withdrew from last Sunday's match against Canada the day before the game because of the injury.
He first suffered the right-foot injury at the start of the season, and it has not come right despite surgery and a lightened programme throughout the season.
Over the past month he has reduced his workload, not taken a full part in practices, and been wearing gym shoes at training instead of boots.
If McCaw does cry off with injury the All Blacks will have lost their two foundations to win the World Cup after key playmaker Dan Carter was knocked out of the tournament last week with a groin injury.
For years, McCaw and Carter, who are the most highly paid players in the country, have been seen as the key men to guide the All Blacks to World Cup victory.
But the side may have to do the job without their two biggest assets.
McCaw's loss would be a huge blow, as he has been the skipper of the side for six years, an inspiration to his team-mates as well as a world-class player.
He became the first man to bring up 100 test caps for the All Blacks in the team's convincing win over France two weeks ago but he may be stuck on the century mark.
Also worrying for Henry is McCaw's obvious replacement, Otago loose forward Adam Thomson, who is struggling with an ankle injury and was unavailable to play against Argentina.