Philippe Gilbert was forced to undergo surgery on a fractured finger after an altercation with an intoxicated man during training, his team BMC Racing Team announced on Friday.
The team said Gilbert was training with Loic Vliegen in Belgium when the two riders were targeted by two intoxicated men in a car.
One of them stepped out and "acted aggressively" towards the riders before fracturing Gilbert's middle finger.
The 33-year-old went to a nearby hospital to receive treatment, where he had pins inserted in his finger.
"Philippe was taken to hospital and underwent surgery to have five pins inserted to secure three small fractures in his middle finger," team doctor Max Testa said in a statement on the team's website.
"He is otherwise fine but will need to take a day or two off the bike.
"After the weekend we should have a better idea of the impact this will have on his Ardennes Classics campaign, but at this stage he should be fine to race. Luckily Loic was not injured in the altercation."
Gilbert said he was feeling fine after surgery but the Belgian admitted he was left shocked by the attack.
"I'm not feeling too bad at all. More than anything I am shocked that this happened as you don't expect anything like this to take place when you head out for a training ride," he explained.