BEIJING — Morgan Hamm is joining his brother on the sidelines for the Beijing Olympics.

The American withdrew from the U.S. men's team with a left ankle injury today, two days before competition is to begin. During the U.S. men's training session yesterday, he appeared to crunch his ankle on an awkward landing on floor and immediately began grimacing. He quickly climbed off the podium to talk to his coach. He went through the rest of the workout, but only did a few more simple moves on floor.

On May 2, his doctor gave him an injection of a glucocorticosteroid, a cortisone-like anti-inflammatory, to treat that sore and swollen left ankle. That resulted in a positive doping test at nationals; the drug is allowed if an athlete gets a therapeutic use exemption, which he failed to do.

He had to have another cortisone shot before he left for Beijing.

"I have been dealing with this for the last year, and it recently has gotten worse here in Beijing," Hamm said in a statement. "Right now I am unable to perform my tumbling skills at the level that I need to. This has an impact on my ability to contribute to the team's goals, and I believe by continuing I would be putting myself at further risk. There are two very capable athletes who can step in and help this team more than I can right now."

The Americans, once considered favorites to return to the medals podium, now have no one with Olympic experience. A replacement was not immediately announced. Sasha Artemev and David Durante are the remaining two alternates, and have been training at the U.S. Olympic Committee's facility at Beijing Normal.

Hamm's withdrawal comes just one day after he said his twin brother, Paul, was considering coming to Beijing to see him compete. Paul Hamm, the reigning Olympic champion, pulled out of the games July 28, two days before the American team left, because he wouldn't be healthy enough. Besides persistent pain from the right hand he broke 2 months ago, the reigning Olympic champion has a strained left rotator cuff, and said it was better that a healthy alternate take his place. Raj Bhavsar took Paul Hamm's place.

The injury is the latest blow for Hamm, who has been plagued by injuries and bad luck the past year. He feared his gymnastics career might be over when a nerve injury left his left shoulder numb in the summer of 2001. Feeling eventually returned — though the shoulder never will be as strong as the other — and he and his brother led the Americans to the silver in Athens, their first Olympic medal in 20 years.

The Hamms took the next 2 1/2 years off after Athens to finish their educations at Ohio State, but decided in February 2007 to return in hopes of making their third Olympic team.

But at the beginning of October, Hamm tore a muscle in his chest, an injury that required a five-month rehab.

"After my injury with my chest, I didn't know if I was able to come back in time," Hamm said yesterday. "I did, which was great."

Hamm made the Beijing team thanks to solid performances at the national championships and Olympic trials. He's one of the best in the world on floor exercise and is one of the best the Americans have on pommel horse, a traditional weakness.

The positive doping test prompted some Hamm drama July 3, when the U.S. Anti-Doping Agency announced the 25-year-old gymnast had accepted a warning for getting a prescribed anti-inflammatory shot without the proper clearance from anti-doping authorities. Hamm tested positive May 24, the second day of the national championships.

Because those results were used to help select the U.S. team, USA Gymnastics had to re-run all of its numbers from nationals and the Olympic trials. After its review, however, USAG said Hamm would still have made the team. The International Gymnastics Federation later said it would not appeal the punishment.

The injury is the likely end of Hamm's career. He and his brother both said they planned to retire after Beijing, and Morgan already has been accepted at the National University of Health Sciences in suburban Chicago, where he will study to become a chiropractor. He is also getting married next spring.

In addition to his silver medal from Athens, Hamm was part of the 2003 U.S. team that won the silver medal at the world championships.