The death of racehorse Venn Ottery after he ran at Newbury is set to be investigated by the Horseracing Regulatory Authority.
Venn Ottery was formerly trained by Paul Nicholls
Venn Ottery, owned by Oliver Carter and trained by Sue Gardner, was put down after fracturing a pelvis on Saturday.
Gardner has since told the Racing Post the 12-year-old ran in the two-mile Game Spirit Chase against her wishes.
HRA spokesman Paul Struthers told BBC Sport: "We need to establish the facts and talk to the individuals concerned."
He added: "Given that it appears Venn Ottery ran against the wishes and advice of his trainer and at the insistence of his owner, we will be formally looking into the matter.
"We need to establish the full facts, whether this could have been avoided and whether any Rules of Racing have been broken.
"Whilst there has been comment about the grade of race Venn Ottery was running in, it is quite likely that he might well have suffered this injury regardless of the grade of the race."
Carter has been unavailable for comment, while Gardner described the horse's death as "heartbreaking."
Venn Ottery, who was having his first race for the trainer, was passed fit to run by a racecourse vet.
Results of a post-mortem carried out after his death will be examined by HRA officials.
The 88-year-old Carter is a permit holder, which effectively licenses him to train, so could potentially have chosen to change the trainer for the race from Gardner to himself.
Struthers said the HRA relies on trainers, who have gone through a licensing process, to have horses' best interests at heart.
Carter caused some controversy within horse racing when he ran Venn Ottery as a rank outsider in both the 2005 Champion Chase and Gold Cup at the Cheltenham Festival.
VENN OTTERY FACTS
He was trained at the time by Martin Pipe, having previously been with the current champion trainer Paul Nicholls.
In 2004, the horse enjoyed a successful campaign when trained by Nicholls, winning four races inside a month and finishing fifth to Azertyuiop in the Champion Chase.
But Nicholls had voiced his concerns before the Newbury race, saying it was an "utter disgrace" he should now be running in such a high-quality contest.
Afterwards, Nicholls was quoted by the Racing Post as saying: "When he goes a mile-and-a-half, pulls up and then has to be put down afterwards, it's terribly sad for the horse.
"I felt very strongly about his running, and hopefully there will be some lessons learned from it."
The nature of jump racing means equine fatalities are a part of the sport.
Triple Cheltenham Gold Cup winner Best Mate died in 2005 after suffering a suspected heart attack following a race at Exeter.
Devon-based Gardner is not one of racing's most well-known trainers, and Venn Ottery was only her second runner of the year.
The ground was too soft and the race too hot
"It was unfortunate as it could have happened on the gallops and, as I instructed, his jockey at Newbury was not pushing him," she told the Racing Post.
"But he should not have been in that race. I didn't enter him or declare him - Oliver insisted that the horse ran and I tried to persuade him not to run.
"If we hadn't turned up with the horse, I would have been fined.
"I told him the ground was too soft and the race too hot, and he said he would take the horse to the races if I didn't."
The HRA has received no official complaint from any party about the running of Venn Ottery.
Going into Saturday, the horse's form had been largely disappointing - he was pulled up twice and fell once in his previous five runs under the Rules of Racing.
The Newbury event was won by Well Chief, who is now favourite for the Queen Mother Champion Chase, one of the feature races at next month's Cheltenham Festival.
Venn Ottery was sent off a 200-1 shot for the eight-runner race and was in last place when he was pulled up by jockey Andrew Glassonbury.
The Racing Post report of the race said: "Venn Ottery has little business in this company these days, and he was pulled up halfway down the far side."