The Finn, whose future has been the subject of intense speculation over the past few days, will not return to F1 duties with Lotus until Friday at Spa.
Raikkonen had been due to speak at his regular Thursday media briefing, where journalists were expected to get his side of the story about why Red Bull decided not to take him and what he hoped to do in 2014.
Instead, a note from his Lotus team said of Raikkonen: "Thursday media call cancelled due to illness - he will be here tomorrow Friday."
Although there was no official word from Lotus about the exact nature of Raikkonen's illness, his absence does have the benefit of meaning he will now not face a barrage of media questions about his future.
Raikkonen's manager Steve Robertson told AUTOSPORT on Wednesday that his driver would be staying at Lotus in 2014 if the team could provide him with the financial and technical guarantees he is after.
"Lotus holds the key to Raikkonen's future," Robertson said.
"If the team can provide him with the answers he is seeking, which will ensure he has a car that can fight for race wins and the championship, then he will stay."