ANAHEIM, Calif. -- The U.S. women's gymnastics team endured its second big loss in two days Saturday when vault specialist Annia Hatch tore ligaments in her left knee during practice.

Hatch was hurt performing a vault and was taken to the hospital. USA gymnastics officials said she completely tore her ACL and meniscus.

The 1996 world-championship bronze medalist joins reigning world balance beam champion Ashley Postell on the sidelines. Postell has a severe case of stomach flu and was scratched by team coordinator Martha Karolyi on Friday.

The women's preliminaries begin Sunday, and the Americans had been considered strong contenders for the gold medal. Now, their hopes aren't nearly as bright, especially considering they lost their best gymnast in their weakest event.

Karolyi replaced Hatch and Postell with first alternate Chellsie Memmel and second alternate Terin Humphrey, the 10th- and sixth-place finishers at nationals in June.

"I think we're going to be fine. We're lucky we have the depth that we have," USA Gymnastics president Bob Colarossi said. "Obviously, we'll be giving something up on the vault. But Terin's exceptionally strong."

Adding to the troubles is that national champion Courtney Kupets is recovering from the illness that got to Postell.

The knee injury is a cruel blow to 25-year-old Hatch, a former national champion in Cuba, who worked her way back to the top after moving to the United States and retiring for five years.

"Annia is probably the best vaulter in the world," Colarossi said. "We were hoping to prove that here."

Instead, Hatch's career is in doubt. Colarossi said the swelling in her knee will have to go down before they can set a date for surgery. Returning from massive knee injuries isn't unheard of in gymnastics -- Jason Gatson of the men's team did it twice. But Hatch already is considered a senior citizen among women in this sport, and the Athens Olympics are just a year away.

"She's obviously distraught," Colarossi said. "Her heart and her mind and her goals were all directed toward competing. It's been a dream for her. This is the kind of thing that isn't supposed to happen."

Humphrey, who turned 17 Thursday, will compete on floor and vault, the same events that were Hatch's strength. Memmel, the gold medalist in the all-around at the Pan American Games, goes from being an alternate to an all-arounder. Kupets, 2000 Olympian Tasha Schwikert and Carly Patterson are the other all-arounders. Surprise national runner-up Hollie Vise will perform on bars and beam.

"We are not done," Schwikert said. "We're going to do this for Annia and Ashley."

Sensing the turmoil her team has been thrown into, Schwikert gathered the team after Karolyi's announcement and gave her teammates a pep talk.

It hardly seemed necessary just a few days ago, when they seemed to have everything going for them.

Patterson, who missed nationals in June with a fractured elbow, has won every meet she has entered since last year's nationals. Kupets is the reigning world champion on uneven bars. Schwikert is a solid, glitzy veteran -- a two-time national champion rounding back into top form.

Being at home helps, too. Anaheim is only a freeway ride from Los Angeles, where Americans cleaned up at the 1984 Olympics. These are the first world championships in the United States since 1991, when Kim Zmeskal won the all-around title.

But suddenly, all the advantages don't seem as big anymore. Instead of looking like gold-medal contenders, the Americans seem to have more in common with the 2000 Olympic team: Injuries and turmoil left that squad scurrying to make lineup changes and convince everyone -- especially themselves -- that everything was OK. They finished fourth, which led to Martha Karolyi replacing her husband, Bela, as leader of the team.

Colarossi said Sydney in 2000 is the farthest thing from anyone's mind.

"This doesn't feel anything like Sydney to me at all," he said. "The single-minded purpose and focus of the women's team the last three years is dramatically different than what it was in Sydney."