According to sources, the Nickelodeon boy bander was cruising through the Hollywood and Vine intersection on his way to the studio ... when a car turned right in front of him.
Henderson swerved at the last second to avoid an accident ... and was violently chucked off his bike in the process.
Remarkably, he was able to stand afterwards ... scraped and bruised from frisbeeing across the blacktop ... but still alive, we're told, thanks in part to his Marc Jacobs jacket ... which he claims saved his back from becoming a mangled mess.
The accident understandably put the kibosh on his trip to the studio ... but Henderson's gonna be just fine.
His bike, on the other hand? Not so much -- it's in the shop for the foreseeable future.