Dunbar, a promising young talent who nabbed the victory in April's under-23 Tour of Flanders, sustained serious head injuries at the U23 Giro d'Italia in June. A crash on stage 1 left him with a severe concussion.
Although he made his way back to racing in relatively short order, he has continued to feel the effects of the crash, riding through both dizziness and nausea while racing at the recent European Championships.
He has decided to skip the rest of the season – including cycling's top one-week race for U23 riders, the Tour de l'Avenir – to recover.
"This was a tough decision for me to make – the World Champs and l'Avenir were big targets for the back half of the season so I'm gutted to miss them. Ultimately, however I need to ensure I get back to 100 per cent for 2018," Dunbar said via the release.
The decision marks the end of Dunbar's time racing with Axeon Hagens Berman, as he is set to join Pro Continental squad Aqua Blue Sport next season.