Gilbert fractured his kneecap on the opening stage of the Tour de France on August 29. He explained it was a 'nonunion fracture' which didn't initially cause him much pain and he was soon back in training and rode the recent Tour de Luxembourg.
However, the pain has worsened in recent days as Gilbert worked on his form at the BinckBank Tour, forcing him to give up hope of riding the Tour of Flanders and Paris-Roubaix later this month.
Gilbert is now recovering at home in Monaco but hopes to recover in time to start the Vuelta a España on October 20.
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"My first priority is to heal completely. I still have a lot of goals in cycling, for next season certainly, but very maybe for this season as well. Hopefully a Tour of Spain participation is still playable, but that’s not yet relevant. What matters now is a full recovery," Gilbert said, explaining how his knee pain has recently increased.
"I quickly got back on the bike after my crash on August 29. Maybe I started again too soon, but the rehab was going well, the motivation and morale were still there, and I really wanted to race.
"I resumed in the Tour du Luxembourg and then competed in two more one-day races, but I still felt pain. This pain became more prominent in the first stage of the BinckBank Tour. I then realized that I couldn't be at my best at the Tour of Flanders and at Paris-Roubaix. These races are even more demanding on the body, the body must be 200 per cent ready."
John Degenkolb will now lead Lotto Soudal in the Classics but he lacks racing after crashing and finishing outside the time limit on stage 1 of the Tour de France.
Lotto Soudal have selected Thomas de Gendt for the Giro d’Italia and so Tim Wellens will also target the Classics, with Caleb Ewan likely to be called in to target Gent-Wevelgem and then Scheldeprijs.
Gilbert will return to the Classics in 2021, when they are scheduled for the usual spring dates.
"Philippe has of course all our support. We took this decision together yesterday. For us it is important that he recovers completely and that he comes back to one hundred percent. The objective now will be to race in 2021 with Phil’s well-known ambition for his classics," Lotto Soudal team manager John Lelangue said.