NAIROBI (AFP) - Chicago marathon champion Patrick Ivuti confirmed Friday he has pulled out of the Boston marathon because of a bout of malaria, dimming his hopes of participating in the Beijing Olympics.

Ivuti, a two-time world cross country silver medallist, was one of the favourites for Monday's race along with his two Kenyan training partners Robert Kipkoech Cheruiyot and Lawrence Saina.

Kenyan officials are hoping to use Boston as a selection arena for the Olympics.

But the 29-year-old, who surprisingly beat two-time world champion Jaouad Gharib of Morocco in one of the closest finishes to the Chicago marathon last October, went down with malaria last week.

"I am extremely disappointed. After training for three months for this race I was very much determined to gauge myself for the Olympics. Maybe I am not lucky," Ivuti told AFP.

Ivuti, three-time Boston defending champion Cheruiyot, Saina and several other training mates including London marathon champion Martin Lel travelled to Namibia last February to train for the Olympics when post-election violence rocked Kenya.

Lel and another Kenyan Sammy Wanjiru have likely booked their Olympic places following their one-two finish in London last Sunday with the remaining one spot possibly reserved for another athlete from Boston.

Ivuti said he was still in contention for the Olympics, possibly citing two other races - one half marathon and a full marathon before the end of May.

Kenyan Margaret Okayo will also miss Boston because of a nagging leg injury which has kept her out competitive sport for the last two years.