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The 22-year-old Palmerston rider pulled out of the Women's Motocross World Championship earlier this week.
It is the third consecutive season she has been cruelly denied a shot at the title.
This time it was a foot injury which derailed her campaign. Last season it was a contentious jury decision. And, in her rookie year, she collided with a photographer who had strayed too close to the track.
Duncan is based in Belgium and could not be reached for comment. But she has been in touch with her mother, Linda Duncan, who told the Otago Daily Times her daughter has found the latest setback hard to accept.
''She was just beside herself as you can imagine - poor wee thing,'' Linda said.
''She was sobbing.
''She is tough and a strong girl but this is just a real kick because she was feeling so confident. And, as she said, she knew she did not have to win [to claim the title] so she could just ride.
''She really did think this year was going to be it. But you never know, do you?''
Duncan has been in dominant form this season. She won five races in row before collecting two second placings in the last round in Italy.
With a 21-point lead at the top of the standings, she had her throttle hand on the trophy.
There was just one niggly concern. She sustained multiple fractures in her right foot during an international event in France in July.
Luckily, it was during a gap in the schedule and Duncan was confident she would be fit in time for the penultimate round in the Netherlands this weekend.
But when she got back on the bike to train, she did further damage to the ligaments around the bone and was forced to withdraw from the championship.
''I've said Courtney Duncan would ride broken to win but it is just not worth it,'' Linda said.
''They said she'll have permanent damage.''
Duncan is getting a scan later this week and, in the worst-case scenario, ''may have to have surgery''.
''But the big picture is, if she rode, she probably would not be able to ride next year. And I honestly don't think with the pain that she is in she would handle a race.''
Duncan has already shown how tenacious she can be by returning from two previous disappointments and is ''determined'' to win the trophy which has proven so elusive.
''It has been her goal to be world champ and she will bloody keep going until she gets it.''