He recounted the embarrassing incident to his fans but joked that at least his bump hadn’t made him forget his first Strictly routine.
“I’ve done something completely stupid,” Walker said alongside a picture of his swollen forehead.
“I left my wallet in the taxi as I checked into a hotel. I ran back out to chase the driver and ran straight into a giant glass door which I thought was open.
“Full deck on the floor, gasps in the restaurant… lump on the head. Thankfully… I still remember the routine.
“I got the wallet back as the driver had stopped for a fag around the corner.”
Walker was inundated from kind comments from fans saying they were sure the Strictly make-up department could work wonders ahead of Saturday night’s launch show.
However, plenty of people also saw the funny side.
“So sorry but the vision in my head is hilarious,” said one fan, while another said it “sounds like a Mr Bean sketch”.
“Sorry to say, but I really hope there's CCTV footage!” said another.
Strictly 2021 is due to begin on Saturday 18th September.
Walker will be up against the likes of Olympic swimmer Adam Peaty, actor Greg Wise, comedian Robert Webb and EastEnders stars Nina Wadia and Rose Ayling-Ellis on the dancefloor.
Watch: Who is Strictly's Dan Walker?