The chef extraordinaire shared a clip to his social media Saturday telling his fans about a recent struggle ... turning a bad experience on his bike into a PSA about the importance of wearing a helmet.

GR starts by telling fans -- who know he loves to ride his bike -- he got into a nasty cycling accident this week that left him in a ton of pain. He says the accident shook him -- and he repeats multiple times he's lucky to be alive.

Gordon shared a ton of thanks to the trauma surgeons who helped him out after the accident before showing fans the injury ... and, it ain't for the faint of heart.

Check out the pic ... Gordon's entire left side is bright purple -- beginning around his hip and extending up his ribs.

Gordon also shared before and after pics of his helmet along with the video ... and, it's clear the thing took the brunt of his fall -- totally caved in at the front.

BTW ... seems like Gordo's in good spirits about the fall -- joking he looks like a "purple potato" in the caption of his post, so clearly his sense of humor's still intact.