Davy Russell and Jack Kennedy will be on the sidelines for “a number of weeks” after sustaining injuries at Limerick on Sunday.
Russell suffered a heavy fall from Doctor Duffy at the first fence in the Munster National and was taken to hospital for precautionary X-rays.
The Cheltenham Gold Cup and Grand National-winning jockey was suspected to have sustained a shoulder injury, but the diagnosis turned out to be much more serious.
Meanwhile, Kennedy, who hasn't long been back in the saddle after recovering from a broken leg suffered at the Dublin Racing Festival in February, fell in the opening Listed novice hurdle.
He tumbled from Etincelle Lioterie three flights from home and also requires a further spell on the sidelines.
An update from the Irish Horseracing Regulatory Board's senior medical officer Dr Jennifer Pugh posted on Twitter read: “Davy Russell sustained a neck injury and has a fracture of his C6 vertebrae. Jack Kennedy fractured his left collarbone.
“Unfortunately they will both be out for a number of weeks.”
