Haile Gebrselassie quit the defence of his Great Scottish Run title after 19 minutes of the half-marathon race.
The former world and Olympic 10,000m champion, 41, was having problems with his breathing when he stopped.
South Africa's Stephen Mokoka won the men's race in a time of one hour, one minute and 25 seconds in Glasgow.
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," Gebrselassie told BBC Sport.
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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.