Daryl Jacob will miss the ride on Intense Raffles in the Boylesports Irish Grand National on Easter Monday due to a broken collarbone.
The 40-year-old was riding Moon Hunter for Henry Daly at Newbury on Friday when he parted company with his mount at the third fence.
He is hoping to be back in time for the Punchestown Festival but will know more next week.
Jacob told SportingLife.com: “It was an unfortunate accident as Moon Hunter clipped heels with a horse in front of him coming down, taking his footing away from him, and I landed on my collarbone.
“It’s fractured in two places and I’ll know more about recovery timelines when I see Geoff Graham, a specialist, next Wednesday.
“The timing is terrible as I was looking forward to riding Intense Raffles in the Irish National and then there’s Aintree just around the corner.
“My motivation is to work hard and be back as soon as I can, hopefully for Punchestown, but I’ll know more on that score next week.”