Keith Mercer looks set to replace the injured Graham Lee on Divers in Saturday's Spinal Research The Atlantic 4 Gold Cup at Cheltenham.
Lee partnered Ferdy Murphy's charge to finish third in last month's Paddy Power Gold Cup as well as steering him to victory in last season's Centenary Novices' Handicap Chase at Cheltenham.
However, he sustained a broken collarbone after parting company with Eliades Run in the Betfred The Bonus King Novices' Handicap Chase at Huntingdon, leaving Mercer to step in for the ride.
Mark Ball, who runs the Let's Live Racing partnership who own Divers, tweeted: "Graham Lee taken to hospital with a suspected broken collarbone. Gutted for him, will miss Divers on Sat, if injury is confirmed.
"Keith Mercer will now ride Divers in the Atlantic 4 Spinal Research Chase on Saturday. Bad luck on Graham but Keith will be a super sub."
Murphy added: "He's broken his collarbone and Keith now takes the ride. It is a blow but it's just one of those unfortunate things.
"The horse jumped it brilliantly and then he was brought down. That's racing I suppose."