LONDON (Reuters) - Twice champion Kauto Star is rated only 50-50 to run in the Cheltenham Gold Cup after a "pretty awful fall" under Ruby Walsh on the gallops last week, according to trainer Paul Nicholls.
The Cheltenham showpiece on March 16 was expected to be a battle between Kauto Star and last year's winner Long Run.
"There is no easy way to say this, but Kauto Star is only 50-50 to make the Cheltenham Gold Cup after a fall schooling," Nicholls wrote in his column on www.betfair.com/paulnicholls on Thursday.
Nicholls reported the horse was still quite sore and stiff and that his participation in the race hung in the balance.
"Even if there is the slightest doubt in our minds, then he stays at home. No question," he wrote.
"He has had the best veterinary and physiotherapy care possible but we hoped that he would be showing more improvement by now.
"Kauto took a tumble when (jockey) Ruby schooled him at the end of last week. I say tumble, but in truth it was a pretty awful fall," he added.
"He is still cantering each day but I can assure you right now that Kauto Star won't be going anywhere near Cheltenham unless we are all convinced ... that he is 110 percent right."
Kauto Star, who won the Cheltenham Gold Cup in 2007 and 2009, is second-favourite for this year's race behind Long Run after beating the champion twice this season.
Writing by Ken Ferris, Editing by Sonia Oxley