Running in the seventh lane, Gay was speeding to the lead in the first turn, but on his 14th stride, something went wrong. He went airborne, fell, then laid on the ground in pain, grabbing his left thigh and grimacing.

Gay already had qualified for the Olympics in the 100 meters, but his availability for the games now will be determined by the severity of his injury.

Though he's the defending world champion in the 200, trials rules call for the top three finishers to make the Olympic team no exceptions.

This was a stunning setback for the 25-year-old sprinter, who last week set the American record in the 100 at 9.77 seconds. In finals, he ran it in 9.68, the fastest time ever recorded, but not a world record because the tailwind was too strong.

Damein White, running in the lane next to Gay, said he saw Gay pull up and thought he saw something fly his way.

"I tried to keep going off the curve," White said. "It kind of threw me off. He just pulled something. He'll be right back. Next year, we've got worlds. You'll see him there."

More urgently, however, are the Olympics. Qualifying for the 100-meter dash starts Aug. 15, and Gay was one of the favorites along with world-record holder Usain Bolt and Asafa Powell, both of Jamaica.

Members of the U.S. track team are expected to leave for the games about 10 to 14 days before their event starts. Gay also was committed for a meet in London on July 25 and was considering running in a couple more events in Europe before the Olympics.

The injury will open up another spot in the 200, where Gay, Wallace Spearmon, Xavier Carter, Shawn Crawford and Walter Dix were considered among the top runners going for only three spots.

"It doesn't really change things on my part," Carter said. "Tyson's a great runner. He's No. 1. Everybody was shooting for him. I'm not going to change anything because he got hurt. I've got to continue doing what I was doing as if he wasn't hurt."

Indeed, the 200 semifinals were set for later Saturday afternoon, and they would go on without Gay.

If the injury is serious, it would be a blow for track, at least on the American scene. He was considered one of the fresh, young faces of a sport that has endured unrelenting doping problems over the past several years. Many were hoping to turn the page this season, and they were hoping Gay, a bit shy, but successful, would be a big part of that.

"He's a champion," said Rodney Martin, who won the heat after Gay fell. "He'll recover. He'll recover."