Justin Gatlin ended a 100m race limping and holding his left thigh just three weeks before the scheduled defence of his world title in Doha.
The 37-year-old American left the track supported by a fellow athlete after finishing fourth in 10.29 seconds in the Croatian capital Zagreb.
Compatriot Michael Rodgers won the race at the IAAF World Challenge meeting in a wind-assisted 10.04.
Gatlin (9.87) has the fourth fastest time in the world this year.
Fellow American Christian Coleman has been quickest in 2019 with 9.81 seconds and is free to run in Doha after potential charges for missing three drugs tests were dropped.
Coleman was second at the 2017 World Championships behind Gatlin, the 2004 Olympic 100m champion who served a doping ban between 2006 and 2010.
In Croatia, Gatlin – who is hoping to compete in his fourth Olympics next year in Tokyo – suddenly winced in pain at around the 80m mark.
