Thistlecrack will miss the Timico Cheltenham Gold Cup and the rest of the season, assistant trainer Kim Tizzard told At The Races.
The 10-year-old looked a potential superstar when winning the 2016 King George VI Chase but a tendon injury sustained last February saw him miss the 2017 Gold Cup and kept him out of action until December.
A lacklustre return over hurdles was followed by a fourth-place finish on his return to Kempton in the King George, but Colin Tizzard's inmate is now set for another prolonged spell on the sidelines.
Kim Tizzard told At The Races: "He was a little bit stiff behind after the King George and he's been off and had X-rays and bone scans - it's gutting.
"He ran a screamer. He jumped really well and we were getting excited that the old Thistlecrack was still there.
"We were going for the Gold Cup - we're gutted. Hopefully he'll have his box rest and come back next season.
"We're gutted for the team, the owners, everyone. We've still got a horse, at the end of the day."
Meanwhile, Un Temps Pour Tout will not be given the chance to win at the Cheltenham Festival for a third consecutive year.
The nine-year-old, trained by David Pipe, has not been seen since he claimed back-to-back renewals of the Ultima Handicap Chase at the Festival last March.
His trainer told www.davidpipe.com: "Sadly, we will be without one of the Pond House standard bearers this year as dual Festival hero Un Temps Pour Tout will not be bidding it to make three in a row this time around.
"His second consecutive victory in last season's Ultima handicap chase under top weight took a long time for him to get over.
"We were aiming to bring him back for the spring but have decided to give him more time and look forward to a full campaign with him next season."
