Olympic 100m champion Marcell Jacobs withdrew at the last minute on Saturday from his long-awaited return to the track in Nairobi because of intestinal problems.
The Italian, who was a surprise winner at last year's Olympics, was due to go head to head with silver medallist Fred Kerley for the first time since Tokyo.
"The Olympic champion made the decision this morning with his staff, due to intestinal problems which occurred yesterday (Friday) in Kenya," wrote the Italian federation on its website a few hours before the start of the Continental Tour meeting.
"Marcell will not report to the starting-blocks today because he remains under observation in the emergency room of Uhai Neema Hospital, under the control of the Italian NGO World Friends," said his coach Paolo Camossi, quoted by the federation.
Six weeks ago, Jacobs stormed to victory to take the world indoor 60m gold in Belgrade, chasing down the American world 100m champion Christian Coleman in the final.
Jacobs is scheduled to compete in a 200m at the meeting in Savona, Italy, on May 18, followed by a five-star 100m on May 28 at the Diamond League meeting in Eugene, Oregon, where the World Championships will take place in July.