Her coach, former World MX1 star Josh Coppins, of Motueka, said on the team's Facebook page Duncan (20) hit the photographer, who was "partly on the track while [she was] leading her race'', at Germany's Teuschenthal motocross venue.
The collision left her with two separate unspecified injuries, and after assessing how she felt overnight, Coppins said the decision was made for Duncan not to race in yesterday's second moto.
"As you can imagine, it has been a very tough decision, but on behalf of myself and Courtney, we would like to thank you all for your support and kind words.
"I can only think this was a bad mistake from the photographer. Needless to say, Courtney is devastated,'' Coppins said on Facebook.
Coppins added that more information would be released today once Duncan's scan results had been received.
Duncan was leading the WMWC by seven points over French former champion Livia Lancelot after the first two rounds of the nine-event championship.
After her injuries forced her to sit out the third round at the weekend, Duncan planned to race again in France on June 5 and Italy on June 26.
Lancelot won both races on the Teuschenthal track, giving her the WMWC lead.
Out of first four WMWC races she contested in Qatar and the Netherlands, Duncan had won three and had a fourth placing.
In the timed practice on Saturday, she was second, 1.7sec behind Italy's defending world champion, Kiara Fontanesi.
- Catherine Pattison
