Mike Teunissen said he started to doubt himself after suffering a heavy crash while training in Tenerife.
The Dutch Jumbo-Visma rider is in hospital after hitting a rock while riding, causing him to crash.
Teunissen said that further examinations have revealed he will need a few more weeks of recovery, throwing his early Classics campaign into doubt.
His Jumbo-Visma team-mate Wout van Aert has shared his concern about the loss of another strong support rider in one-day races, after Tom Dumoulin announced he would be taking a break from professional racing.
Teunissen, who wore the yellow jersey in the 2019 Tour de France after winning the opening stage, said: “I would normally consider myself as an optimistic person and a good bike handler, the past days I have started to doubt both. Last year was tough but I am now facing another setback due to a fall on a training camp in Tenerife.
“My teammates saw it happen and called it really bad luck, I hit a poorly visible rock and crashed.”
The 28-year-old added: “Medical examinations in the Netherlands showed that I will need a few weeks to recover, but hopefully I will find the strength to be back fighting again soon.”
He did not reveal any further details about his injuries.
Teunissen was likely to be a huge asset to Jumbo-Visma and Van Aert in the spring Classics, where Van Aert will be targeting Strade Bianche, Milan-San Remo and the cobbled Monuments, the Tour of Flanders and Paris-Roubaix.
Van Aert’s coach said the star rider is currently in good enough shape to compete in the finals of the biggest races, but not to win, as he is currently around 2kg above race weight after gaining a lot of muscle during his cyclocross season.
Van Aert told Belgian newspaper Het Nieuwsblad: “It’s not going in the right direction.
“With Mike and a good Tom Dumoulin we had three pawns who could ride a final in every Classic. I hope we don’t lose Mike all spring, but of course this is not good.”
But Van Aert pointed to new team-mates Edoardo Affini and Nathan Van Hooydonck, along with Timo Roosen and Pascal Eenkhoorn, as strong support in one-day races.