Niall Madden was sent to hospital with a suspected fractured arm after a fall in the fourth race at Kilbeggan.
Madden had stepped in for the injured Paul Carberry on Carlesimo but his mount crashed out at the first fence.
"I've sent him to hospital for x-rays on his right arm with a suspected fracture," said Turf Club Medical Officer Dr Walter Halley.
Carberry was earlier stood down for 48 hours following a fall from Asigh Pearl in the second race.
He needed stitches over his eye after the spill and also suffered bruising to his lower back.
