Edward O'Grady, his trainer, said yesterday: "Sound Man was lame on his near-hind after exercise on Sunday. He has not been sound since and having consulted with the owners we regrettably decided to withdraw him from the Queen Mother Champion Chase.
"There is no decision yet as to whether he will race again this season. We don't know enough about the injury."
Sound Man won the Tingle Creek Chase at Sandown in December, but was a modest third behind Strong Promise and One Man in the Comet Chase at Ascot on his latest start.
O'Grady will still have two runners at the Festival, a meeting at which he has sent out 15 winners since 1974.
He will send Time For A Run for either the Astec Buzz Shop Chase or Kim Muir Chase and will saddle What A Hand in the Foxhunters' Chase.
Ladbrokes responded to the news of Sound Man's withdrawal by cutting the price of last year's winner, Klairon Davis, from 9-4 favourite to 15-8. Viking Flagship, seeking his third win in the race, is now 5-2 second favourite with both Ladbrokes and William Hill.
QUEEN MOTHER CHAMPION CHASE: Ladbrokes: 15-8 Klairon Davis (from 9-4), 5-2 Viking Flagship (11-4), 4-1 Strong Promise, 5-1 Ask Tom, 14-1 Arctic Kinsman (16-1), 16-1 others; William Hill: 2-1 Klairon Davis (9-4), 5- 2 Viking Flagship (11-4), 4-1 Ask Tom (9-2), 9-2 Strong Promise (5-1), 12-1 Martha's Son, 20-1 others; Coral: 9-4 Klairon Davis, 9-4 Viking Flagship, 7-2 Ask Tom, 9-2 Strong Promise, 14-1 Arctic Kinsman, Martha's Son, 20- 1 others.
n The track at Plumpton will be inspected at 3.30pm today to determine whether Friday's card can go ahead.