Ruby Walsh was stood down for the rest of day two at the Cheltenham Festival after he suffered a heavy fall during the second race.
The winning-most jockey in Festival history sustained what appeared to be a leg injury when he parted company with Al Boum Photo in the RSA Insurance Novices' Chase.
Walsh will need medical clearance before he can take up any further rides at the last two days of the meeting.
The British Horseracing Authority's stewarding team tweeted: "Following examination by doctors, Ruby Walsh has been stood down for the rest of the day. He would need to pass a further medical examination by Doctors before taking any further rides at the Festival."
Walsh was due to partner Douvan in the big race of the day, the Betway Queen Mother Champion Chase, with that mount subsequently taken by Patrick Mullins.
The 38-year-old rider only returned to competitive action last Thursday after he suffered a broken leg at Punchestown on November 18.
Walsh rode two winners at the Cheltenham Festival on Tuesday - aboard Footpad in the Arkle Trophy and Benie Des Dieux in the Mares' Hurdle.
Walsh was taken to hospital for further examination, and Douvan's owner Rich Ricci said: "He's been taken to hospital with a suspected broken leg. It's a shame and I hope he's OK.
"It looks like it's the same leg."