The boy, identified as Dylan, wondered why a wound on his leg would not heal and sought help from the Saint-Privat de Béziers health clinic near his home in the Hérault region.
Doctors examining the wound discovered a seven-centimetre long brake lever buried beneath the skin, according to a report from Le Midi Libre on Thursday.
The newspaper reported that after the bike accident occurred the boy was treated too hastily.
Doctors stitched up the deep wound without checking to see if there was any debris inside.
It was a mistake that caused the boy four months of pain because the wound would not heal, the newspaper said.
The surgeon who recovered the brake lever this week was astonished by the find.
“I’ve never seen that,” he was quoting as saying to Dylan’s parents by Le Midi Libre.
The discovery was made after a check revealed a part of Dylan’s trousers was sticking out of the wound.
A decision was made to operate and the bike part was subsequently found and removed.
Judging from a photo of the victim, Dylan appears to be recovering well.