A hamstring injury has forced Australia's Olympic champion Jared Tallent to pull out of the 20km walk.
Tallent will still defend his new Olympic title in the 50km race, which is a week later, but he was worried he would aggravate a minor hamstring problem if he competed in the hard and fast shorter walk.
I just have a little niggle, it's nothing serious. I just don't want to risk it. It's just a precaution and I don't want to risk the main aim being the 50k," Tallent said.
"Having a hard race for the 20km might distress the injury a little bit.
"It's definitely not the end of the world, I haven't done the work for the 20k to be competitive anyway. The training for the 50k is very different.
Australians Dane Bird-Smith and Rhydian Cowley will be in the 20km walk field with Bird-Smith a strong medal chance.
Tallent made the decision soon after he arrived at the team's camp in Florida and consu
Tallent won bronze at the Beijing Olympics in 2008 in the 20km walk and backed that performance up with silver in the 50km walk. Since then he has proven a far stronger long event walker.
At the London Olympics he was 7th in the 20km and then won silver in the longer event, which became gold four years later after the Russian was disqualified.
He was 26th in the 20km walk at the World Championships in Beijing last year but rallied in the longer walk a week later to win silver.
"Realistically it was more of a last hit-out, to go through the call room, and be on the course but now I have so much experience, I have done it so many times at world championships and big events. I will be fine," he said.
"I decided just to keep it safe and focus on the main game. There's plenty of time, all the hard work has been done in St Moritz, so it's just being [careful], that's all."
lted team doctors and coached. He had come to the US from a solid period of altitude training at St Moritz in the Swiss Alps.
Sign up for our newsletter to stay up to date.