"He has a little bit of a strain in his right hamstring and he didn't want to risk it," his agent Mark Wetmore told Reuters. "He was trying to warm up and he couldn't fully extend."
Lyles was one of the favourites to win the event after running 19.90 seconds last month in Shanghai, the third fastest time of the season.
"He could have run but it would have just been an unnecessary risk to take for a 19-year old," Wetmore said.
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Lyles developed the sore hamstring at the Shanghai meeting and had not run until the U.S. championships. He won his first-round race in Sacramento in 20.54 seconds on Saturday.
"It's unfortunate, bad timing," said Wetmore, who added that it was best for Lyles to withdraw.
(Editing by Ken Ferris)
