The 28-year-old, a former winner of Milan-San Remo and Paris-Roubaix, was set to be Germany's team leader and one of the favourites for the Bergen course, but it emerged on Sunday morning that he will not ride, with the German Cycling Federation (BDR) citing "health problems" and "respiratory problems".
After leaving the Vuelta, Degenkolb returned to racing earlier this month at the Brussels Cycling Classic and GP de Fournies one-day races, and this week he rode four stages at the Tour of Denmark - often in terrible weather conditions - but did not finish the final stage on Saturday.
Johannes Fröhlinger from Team Sunweb will take Degenkolb's place in Germany's nine-man team.
"For me it's a honour to be selected as the captain of the German road Worlds national team. I don't take that for granted. It's something special. It shows the respect of the BDR, the trust from the trainers and stuff and of course from the team mates. It's a huge responsibility. I thank everybody for this one," Degenkolb wrote in a statement on his Facebook page.
"But I have the same responsibility for all of them and my team deserves the maximum honesty. After I left the Vuelta due to a bronchitis I could return very fast back on my bike, back into training and as well back into racing. In these races it turned out that I am not in the shape as before, not in the shape to fullfil the leading role at the world cups elite race. A role I expect from myself and my teammates and the fans expect that from me as well.
"Believe me, it was not an easy decision to announce today that I won't start in Bergen. But it is the right one in regard of the team, in regard of the BDR and as well in regard of myself. I wish the full German team maximum success at all the races in the next week in Norway and keep for all of them the fingers crossed."
Degenkolb has endured a difficult season. He has racked up a huge number of placing in the Classics and Tour de France sprints but has failed to take a win since stage 3 of the Dubai Tour in February.
He fell ill early in the Vuelta and, after trying to continue in the race but struggling to recover, he and the Trek-Segafredo team decided it was best to rest up and recover for the World Championships. Degenkolb was named as team leader of the German squad because the rolling circuit in Bergen seemed to suit him perfectly.
However, the Trek-Segafredo team doctor Dr. Jens Hinder advised against Degenkolb racing in Bergen.
"John's airway problem, which forced him to struggle at the Vuelta, have not subsided in the recent races and further investigation is needed. That is why, from a medical point of view, it is not advisable to participate in the World Cup,” he said, according to the statement from the German Cycling Federation.
The German team will try to find an alternative race strategy for the elite men's road race, with Tony Martin (Katusha-Alpecin), Marcus Burghardt (Bora-Hansgrohe) and Simon Geschke (Team Sunweb) likely to be given leadership roles. Also in the nine-man team are Nikias Arndt (Sunweb), Paul Martens (LottoNL-Jumbo), Nils Politt (Katusha-Alpecin), Jasha Sütterlin (Movistar) and Rick Zabel (Katusha-Alpecin).
"This is a big blow to us because John Degenkolb was a good captain. Nevertheless we have nine highly motivated strong riders at the start, who can help shape the race, "said German Cycling Federation vice-president Udo Sprenger.
"We have a strong team and it's hard to understand our strategy without a firm captain. That could be our strength."