“It’s due to an old splint that has been dormant. It’s never bothered him before and, typically, it rears its ugly head now.”
Altior is looking to become the first horse since Badsworth Boy to win three Queen Mother Champion Chase titles.
Last year’s Gold Cup winner suffered his first career defeat over jumps at Ascot in November.
But Altior then returned to win his favoured two miles in the Game Spirit at Newbury just last month.
The 2020 Cheltenham Festival takes place from Tuesday, March 10 to Friday, March 13.