Dunedin-based Trek World Racing rider Justin Leov was 21st in his final world championship event before retiring.
MacDonald, the world No 5, fell behind the clock in the first section of the 2.4km track at the Leogang Bike Park in the Alps.
The 20-year-old pushed hard, clocking 3min 26.651sec, to finish 5sec behind the winner.
The MS Mondraker professional was the only Kiwi to finish in the top 10 on the course that had dried and rutted after two days of rain.
Last year's bronze medallist, Sam Blenkinsop (Wanganui), placed 11th, Lapierre International team-mate Cameron Cole (Christchurch) finished 16th, and an injured George Brannigan (Hawkes Bay, DeVinci Global) was 26th.
Auckland's Sophie-Marie Bethell and Nelson's Veronique Sandler finished 24th and 26th respectively in the elite women's competition.
Coatesville teenager Sophie Tyas placed eighth in the junior women's contest, while the best of the junior men was Takaka's Reece Potter, who was 18th.
King's High School pupil Dan McCombie gained valuable experience with a 60th place in the junior men's race in 4min 1.728sec.
The action moves to nearby Saalfelden for this week's cross-country world championships, which begin on Friday.
