Haile Gebrselassie (Ethiopia) quit the defence of his Great Scottish Run title 19 minutes into the half-marathon race in Glasgow.
The former world and Olympic 10,000m champion, 41, was having problems with his breathing when he stopped.
South Africa’s Stephen Mokoka went on to win the men’s race in a time of one hour, one minute and 25 seconds.
Kenya’s Edna Kiplagat took the women’s title in a race record 1:07:57, with Scotland’s 2013 winner Susan Partridge finishing fifth.
Gebrselassie won the men’s race last year in the fastest time ever recorded in Scotland for the 13.1-mile half-marathon distance.
His time of 61 minutes and nine seconds was also a world age-group record.
“The training I’ve done has been very good but I knew things were not quite right when I did my speed work,” Gerbrselassie told BBC Sport.
Mokoka, 29, surged clear to win by seven seconds from Stephen Chemlany, with Mark Kiptoo just behind, while Callum Hawkins was the top British finisher in sixth on his competitive half-marathon debut.
Kiplagat, the two-time world and reigning Olympic marathon champion, was a clear winner of the women’s race, beating her compatriot Caroline Kilel by 56 seconds.
Around 30,000 participants of all ages started Scotland’s biggest running event, taking part in either a 10,000m or half-marathon challenge through the heart of the city.
Source: BBC Sport