Ruby Walsh was forced to give up his ride on leading fancy On His Own in the John Smith's Grand National after a fall from Zarkandar at Aintree.
The Irish jockey was stood down for the rest of the day following his tumble at the sixth flight in the John Smith's Aintree Hurdle.
The British Horseracing Authority tweeted: "Ruby Walsh has been stood down for the rest of the day on medical grounds after assessment following fall on Zarkandar."
Two years ago, Walsh missed the National and was out for several months after being badly injured in the same race in a fall from Celestial Halo.
Paul Townend switched to On His Own in the big race, with Andrew Tinkler replacing Townend on The Midnight Club.