"Isaac Makwala was withdrawn from the men's 400m (Final) due to a medical condition on the instruction of the IAAF medical delegate," world athletics' ruling body said in a statement.
Makwala was withdrawn from the first round of the men's 200m yesterday for the same reason, but insisted Tuesday he was ready to run the 400m, scheduled for 2050 GMT, before the IAAF stepped in.
Public Health England said 30 athletes and support staff had been affected at a central London hotel, with two cases confirmed as being the norovirus bug.
"We have so far been made aware of approximately 30 people reporting illness and two of these cases have been confirmed as norovirus by laboratory testing.
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"PHE has been working closely with the London 2017 organisers and the hotel to provide infection control advice to limit the spread of illness."
Norovirus is often caught through close contact with someone carrying the virus or by touching contaminated surfaces or objects.
Norovirus, which brings on diarrhoea and vomiting, is rarely serious, with most people making a full recovery within one or two days, without treatment.