Usain Bolt will not ease off in his world championships preparations because American rival Tyson Gay is out of the competition, the Jamaican said on Saturday.

"I will not relax at all, as I know and expect strong challenges from even my own teammates in Jamaica and the Caribbean," triple world champion Bolt said in a statement issued by his publicist.

Bolt extended his sympathy to world 100-meter silver medalist Gay, who scratched from the United States trials because of hip problems, but said his schedule and build-up for the August 27-September 4 meeting in Daegu, South Korea, would not change.

The 24-year-old will defend both his 100 and 200 titles from the 2009 worlds in Berlin, where he smashed his own world records from the 2008 Beijing Olympics.

With a bye to both events at Daegu as title-holder, Bolt sat out of the Jamaican trials over the weekend where former 100-meter record holder Asafa Powell won the event.

Bolt said he would return to competition on July 8 with a 200-meter run in Paris.

In Eugene, Oregon, Allyson Felix kept alive the possibility of a bid for a world championship double in the 200 and 400 meters as she clinched her first national 400 title at the US trials on Saturday.

Felix, challenged by runner-up Francena McCorory down the straight, ran strongly to the finish in 50.40 seconds and become the first woman to win US titles in the 100, 200 and 400. "I knew it was going to be racing home," said Felix, who has five US 200 titles and added the 100 last year. "I wanted to be in position to use my speed."

McCorory clocked 50.49 to beat world indoor champion Debbie Dunn (50.70).

Felix, who will defend her 200 title in Daegu, said she was undecided on whether she would attempt the double, but hoped to make the decision soon. She also left open the possibility of doing as many as four events at the world championships and confirmed she would attempt the 4x100 and 4x400 relays.