Walsh was riding Al Boum Photo in the Mrs J Donnelly black-and-yellow colours and looked in contention for a place in the latter stages while favourite Presenting Percy was streaking clear of the field.
But his ride fell at the penultimate fence and while the horse himself was up and running quickly, Walsh himself stayed down.
Green screens were put up around the jockey for privacy but he was eventually helped up and left the track without an ambulance.
Express Sport understands Walsh was then taken to hospital with a leg injury and while sources claim it is unlikely he will ride again this week, the 41-year-old could in theory be allowed to take up his rides on Thursday and Friday if he passes a medical examination.
The extent of the injury is currently unknown but Matt Chapman on ITV’s coverage revealed that Rich Ricci, owner of a number of Walsh’s rides, had claimed the jockey had broken his leg.
Ruby Walsh was on board Al Boum Photo when he fell
“Rich Ricci has just texted me,” Champan told ITV.
“He has said that in his opinion or at least as far as he is aware, Ruby Walsh has broken his leg.
“That means Patrick Mullins will ride Douvan and Paul Townsend on Min.
“That is the latest from Rich Ricci who has just called me to give us that news.”
Walsh, who is the most successful jockey ever at the Cheltenham Festival, has only just come back from an horrific leg break that he suffered at Punchestown last year.
And he spoke ahead of the Festival of his delight at simply being able to ride again.
“It’s great to be back. As regards tactical awareness and match fitness, the horse is the one that’s doing all the running,” Walsh said.
“Yes, race riding is a huge physical exertion, but the jockey is the tactician.
“It’s about mental sharpness, not physical. The last time I came back, I hadn’t done much riding.
“I was out longer in 2011 after injuring the same leg – that year, I won on three horses on day one of Cheltenham. I’d settle for that now!”