The 20-year-old Yamaha rider is due to arrive in Dunedin on Thursday for surgery on her thumb after crashing into a photographer on the Teuschenthal track in Germany on Saturday.
"I will be back. This won't stop me, I promise you that,'' Duncan wrote in an email to the Otago Daily Times yesterday.
Duncan went into the third round of the Women's Motocross World Championship with a comfortable lead after three wins in four of the previous races.
Her New Zealand coach, former motocross star Josh Coppins, said it was a "huge judgement error on behalf of the photographer'', who was standing on one of the track's jumps.
Duncan was leading the first race of the weekend and was just two laps from the finish when the incident happened.
"She actually hit the photographer with her handlebars as she jumped,'' Mr Coppins said.
She injured her thumb and her ankle in the crash that followed and after assessing her injuries overnight the decision was made for her not to race on Sunday.
"Courtney's championship season is done,'' Mr Coppins said.
Duncan posted a photo on Facebook yesterday of a female photographer directly in her path and described it as "the moment that cost me the championship. It's devastating, to say the least''.
"It sucks to go out like this but there is nothing we can do about it now. I've now got to focus on getting healthy and recovery.''
Mr Coppins was awaiting official word on the incident and the repercussions for the photographer, but did not think there would be any financial compensation.
"Currently, I think that the promoter is working through the issue. So far we haven't heard anything.
"An apology would be nice but, regardless, our focus is on Courtney.
"We are already planning our comeback later in the season to show what could have been,'' he said.
Duncan hoped to race in the final two world rounds in Switzerland and Holland in August.
