"We are trying to find the reason why," a spokesman for the organisers said. "It's disappointing to lose the defending champion, of course, but it will not detract from the event."
The world champion, Peter Easmussen of Denmark, withdrew on Sunday with an ankle injury. Dong is the third seeded player to pull out in the past few days, after Rasmussen and his Danish team mate, Thomas Stuer-Lauridsen.
Some Asian countries have sent smaller squads to this year's championships because of financial hardship, but officials had been confident all the big names would be present. Although the sport recently expanded to a record 137 affilated countries, its leading nations and several of its most important tournaments have been badly hit by the withdrawal of sponsors and the collapse of Asian currencies.
Two big tournaments, the Korean Open and the Thailand Open, have already been cancelled, and a third, the Indonesian Open at Sulawesi, in August is at risk. The Thomas and Uber Cups finals, scheduled for Hong Kong in May, may be switched to England.