The TV presenter, 44, has been training for the BBC show ahead of Saturday’s curtain raiser, which will see the stars teamed up with their professional partners.
Walker said he hit his head on a “big glass window” on Thursday and was taken to hospital a day later after “feeling a little wobbly”.
And he thanked his Strictly partner, who will remain a mystery until Saturday’s pre-recorded show is broadcast, for making sure he was OK.
Alongside a selfie from hospital, Walker wrote: “Bit of head-based drama today! After whacking my noggin on the big glass window yesterday I got sent to A & E today because I was feeling a little wobbly.
“A lovely nurse at Barnet Hospital called Karina checked my vitals and 6ft 9 Consultant Erik Witt gave me a CT scan to check for a bleed on the brain. Thankfully… all ok.
“I’ve got to rest for a couple of days – so I’ll be a bit behind – but ready to dig in again next week.”
Walker, who presents BBC Breakfast, added: “A timely reminder of how amazing the NHS is and, even though I’m not allowed to tell you who my Strictly pro is… I can tell you that she waited for hours in the car park to make sure I was ok. Whatever happens on the telly… she has a friend for life.”
Walker, who has three children with wife Sarah, said he agreed to do Strictly because he wanted a “giggle” after reporting on difficult news stories during the pandemic.
The 15 celebrities taking part in the new series include Olympian Adam Peaty, rugby star Ugo Monye, TV presenter Judi Love and former Bake Off winner John Whaite, who will be part of a same-sex pairing.
Strictly Come Dancing returns to BBC One tonight.