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 were quick to maintain that the 41-year-old could in theory be allowed to take up his rides on Thursday and Friday if he passes a medical examination.
However, a statement from his camp this evening has confirmed that Walsh is out of the Festival for this year.
“Unfortunately he has aggravated a recent leg injury and will see his consultant in Dublin next week for further assessment,” said his sister Jennifer, who also acts as Ruby’s agent.
The full extent of the injury remains unknown but Matt Chapman on ITV’s coverage revealed that Rich Ricci, owner of a number of Walsh’s rides, had claimed in the immediate aftermath that the jockey had broken his leg.
“Rich Ricci has just texted me,” Chapman 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.”
Trainer Willie Mullins would not be drawn on the exact nature of the injury but admitted that he could be out of the Festival
“It looks as if it’s the same injury as before. Its right on the same point, but until we get the X-rays we cant be sure,” Mullins said.
“It’s hugely disappointing for Ruby and everyone. That’s sport. We have to pick up and move on. He’s got an injury and I’m hoping he’ll recover from it.”
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!”