Kenya's double Olympic champion Eliud Kipchoge said "not every day is Christmas" after his Paris Games preparations hit a snag with a 10th-place finish at Sunday's Tokyo Marathon behind winner Benson Kipruto.
The 39-year-old Kipchoge faded badly at around the 20km mark and crossed the line in 2hr 6min 50sec.
Kenya's Kipruto won in a course record 2:02:16 ahead of countrymen Timothy Kiplagat (2:02:55) and Vincent Ngetich (2:04:18).
The race was taking place less than a month after world record-holder Kelvin Kiptum died when his car crashed into a tree in Kenya.
Kipchoge will attempt to win his third straight Olympic marathon gold later this year and he said it was "too early to say" what shape he will be in at the Paris Games.
"That's how it is – not every day is Christmas Day," he told Japan's Nippon TV.
Kipchoge said "something happened in the middle of the race", without elaborating further.
He dropped back dramatically to leave Kiplagat, Kipruto and Ngetich fighting it out in the leading pack.
Kipchoge continued to struggle as the race wore on and had dropped out of the top 10 by the 35km mark.
"I will go back, relax and start training," he said.
KEBEDE SECURES WOMEN'S VICTORY
Ethiopia's Sutume Asefa Kebede won the women's race in 2hr 15min 55sec, ahead of Kenya's defending champion Rosemary Wanjiru (2:16:14) and Ethiopia's world champion Amane Beriso Shankule (2:16:58).
Sifan Hassan of the Netherlands was fourth after clocking 2:18:05.
Kiptum was killed at the age of 24 on 11 February, just months after he beat Kipchoge's world record to set a new mark of 2:00:35 in Chicago.
Kiptum and Kipchoge were expected to face off for the first time at the Paris Olympics.
The Tokyo Marathon was Kipchoge's first race since Kiptum's death and he was on pace to reclaim the world record until he tumbled out of contention.
Kipruto took over the lead from Kiplagat around 30km in and powered towards the finish for a new personal best.
Kiptum was driving in the Rift Valley, the heartland of Kenyan distance running, when his car careered off the road.
Police said Kiptum and his Rwandan coach Gervais Hakizimana were killed on the spot while a woman passenger was injured.