Dalilah Muhammad, the reigning 400m hurdles world champion and gold medallist at the 2016 Rio Olympics, will miss the US trials with a hamstring injury that she expects to be healed in time for her title defense.
As reigning champion Muhammad has a bye into the event at the World Championships in Eugene, Oregon, in July.
Normally US qualifying procedures would require her to race at least one heat of one event at trials to use her bye, but she was able to receive a waiver to opt out of the meeting that starts Thursday on the same Hayward Field track that will host the championships.
"It just wasn't worth me pushing," Muhammad said Wednesday at a pre-event press conference.
"I just kind of minorly stretched my right hamstring," Muhammad said of the injury. "Kind of just tweaked it a little bit, about two weeks ago."
Muhammad had been set for another showdown with fierce rival Sydney McLaughlin, who seized Olympic gold ahead of Muhammad in Tokyo last year in spectacular fashion, smashing her own world record to take gold in 51.46sec.
Muhammad posted the second-fastest time in history in taking silver in that race.
But she hasn't raced since May 21, withdrawing from a planned race on June 12.
Muhammad however said that other than this recent setback she felt like she was approaching peak form, after battling Covid-19 and injuries to make it to Tokyo last year.
"I feel like I'm getting back to prime fitness level, unfortunately we're probably just going to have to wait til worlds to see."
McLaughlin, meanwhile, is entered at the trials where a top-three finish will clinch a place at Worlds. She was runner-up to Muhammad at the 2019 World Championships.