Jockey Davy Russell hopes to return at next month's Punchestown Festival after breaking his arm in a fall.
The 35-year-old did not break a leg, as initially feared, in Saturday's incident at Gowran Park.
Adrian McGoldrick, chief medical officer for the Irish Turf Club, said Russell would have surgery on Sunday.
Russell had earlier revealed he had lost the ride on Lord Windermere, with whom he won the 2014 Cheltenham Gold Cup for trainer Jim Culloty.
The jockey will miss the Irish Grand National at Fairyhouse on 5 April and the Grand National at Aintree five days later, in which Culloty intends to run Spring Heeled.
Russell, who rode two winners at this year's Cheltenham Festival, was injured when his mount Feenakilmeedy fell in a beginners' chase.
"He's going to be operated on. He's broken his left ulna which is the smaller bone in his arm," said McGoldrick.
Russell, who also won the 2013 RSA Chase at the Cheltenham Festival on Lord Windermere, said he was "very disappointed" to lose the ride after the horse was pulled up when defending his title on 13 March.
"After the  Gold Cup, Jim told me he didn't want me riding his horses," he told the Irish Daily Star.
"He wasn't happy with the ride I gave the [Lord Windermere] and he said he wanted a change."