The eight-year-old, trained by Mark Bradstock, made a brilliant return to action at Kempton earlier this month but spread a plate yesterday morning.
His participation in the Hennessy is now dependent upon Coneygree proving his fitness in time for a “proper gallop” on Saturday.
Sara Bradstock, wife and assistant to the Oxfordshire handler, said: “A nail slightly pricked his foot and he has spread a plate. These things can resolve themselves, though, and it might be that by Wednesday he is back all signing, all dancing.
“If it doesn’t resolve itself he will get an abscess and it will take longer to heal. We need to warn people about the Hennessy as he needs to be doing a proper gallop on Saturday.
“It’s only something very small, but you cannot take any risks with a horse of his magnitude.”
Meanwhile, Cheltenham Festival winner Teaforthree has been retired.
Trained by Rebecca Curtis, the 11-year-old’s finest hour came in the 2012 Diamond Jubilee National Hunt Chase when he pulled two lengths clear under JT McNamara.
Teaforthree twice competed in the Grand National at Aintree, finishing third in the 2013 renewal, but time has now been called on a career which had recently taken him into the hunter chase division.
Michael Heard faces a lengthy spell on the sidelines after he suffered a bad back injury following a nasty tumble from Willem in a conditional jockeys’ handicap hurdle at Cheltenham on Sunday. The young jumps jockey underwent scans after being detained in Gloucestershire Royal Hospital for further assessment after he was unshipped from the David Pipe-trained five-year-old at the fifth-last flight.