Dual Queen Mother Champion Chase winner Master Minded has undergone surgery on a serious tendon injury.
The eight-year-old, from the Paul Nicholls yard, suffered the injury in Monday's King George VI Chase at Kempton and was taken for treatment.
Nicholls said on Twitter on Tuesday morning that the horse was in a comfortable condition.
The trainer added that the injury was "career-threatening but hopefully not life-threatening".
As well as his Cheltenham victories in 2008 and 2009, Master Minded has twice won the Tingle Creek Chase as well as the Melling Chase at the Aintree Grand National meeting earlier this year.
He won last month's Amlin Chase at Ascot for the second time to bring his career earnings to £1.16m from 28 races.