Dutch rider Theo Bos was forced to abandon the Rotterdam Six Day on the eve of the race's final night after falling ill.
Bos and partner Peter Schep were in the lead after Sunday's racing, having taken a one-lap lead over the rest of the field.
Bos began to feel unwell on Monday when the team fell to second place behind new leaders Iljo Keisse and Kenny De Ketele. Bos showed a high fever today, his team said.
Bos is the second rider to drop out of the Rotterdam Six Day with illness. Swiss rider Franco Marvulli abandoned on the third night, while Wim Stroetinga dropped out after breaking his collarbone in a crash.
Stroetinga is due to have surgery to repair his fractured clavicle, and will not participate as scheduled in the Beijing World Cup this month.