Justin Gatlin pulled up, grabbing his left leg in a 100m in Zagreb, Croatia, on Tuesday, three weeks before he defends his world 100m title in Doha.
Later tests on his hamstring were negative, and he was expected to return to training later this week, his manager said, according to Reuters.
Gatlin similarly trotted across the finish line of a 200m in Grenada on April 13 after grabbing at his left thigh. His manager said then that it was a cramp. He reportedly suffered a right hamstring injury in a May 2018 relay, too.
Gatlin came back this summer to break 10 seconds in three straight meets, becoming a medal favorite for the world championships behind countryman Christian Coleman.
But last week he was fourth at the Diamond League Finals in Zurich, his worst result this season, putting into question his status as the top challenger to Coleman.
Earlier Tuesday, Allyson Felix placed second in the 400m in 51.67 behind world champion Phyllis Francis, who clocked 51.02. Felix raced her second meet since Nov. 28 childbirth by emergency C-section.
Felix is expected to be at worlds, marking her record-breaking ninth world outdoors team. She currently shares the U.S. record of eight teams with retired high jumper Amy Acuff, according to the OlyMADMen.
Felix could be in the 4x400m and mixed-gender 4x400m relay pools but not the individual 400m at worlds, given she placed sixth at the USATF Outdoor Championships in July. Her best time this season, from the USATF Outdoors semifinals, is 51.45, ranking her 40th in the world this year.
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