Fabian Cancellara faces time out after fracturing his lower back during the E3 Harelbeke in Belgium, Trek Factory Racing have confirmed.
The 34-year-old Swiss rider suffered the injury following a crash involving Lars Boom and John Degenkolb during the Haaghoek cobbled section of the race on Friday.
Cancellara attempted to continue after the accident, but the pain became too much and he was taken to hospital to be assessed.
"X-rays have confirmed the worst," Trek tweeted. "Two fractures of the vertebrae in his lower back for Fabian Cancellara means no spring campaign."
As a result Cancellara – who has won eight Tour de France stages during his career – is likely to miss the chance to defend his Tour of Flanders title, ending a run of two successive wins.
"There was a massive crash on the Haaghoek," team director Dirk Demol told Sporza. "He severely hurt his lower back, his left wrist and hand.
"I'm also worried about [him making] the next races. He's a fighter. If he can then he will race."