County Hurdle favourites Power Elite and Al Eile are the latest leading contenders to be ruled out of races at the Cheltenham Festival.
Power Elite is out with a bruised foot, while Al Eile will only run in Tuesday's Champion Hurdle.
Ambobo, favourite for the Royal & SunAlliance Novicesī Hurdle, also misses out because of a leg problem.
Nicky Henderson's Calling Brave is another sidelined - joining Best Mate, Ollie Magern and Kauto Star.
Ambobo was as low as 7-2 for the SunAlliance, but confirming he will miss the race, Herve Barjot, spokesman for owner Sean Mulryan, said: ""He is lame on his right front joint. He is not 100 per cent so he can't run.
"He should be able to run again this season and we might be able to get him to Aintree.
"We are naturally very disappointed, but that is life."
Ambobo shot to prominence for the Festival after powering home at Cheltenham to easily land a Grade Two event in January, when he had the smart Brewster and Mephisto in second and third.