The six-year-old's death led to a call to by Mark Coton, chairman of the National Association for the Protection of Punters, for a drastic improvement in stable security.
Coton, who also runs a tipping service named the Winning Line which had selected the horse, received telephone calls regarding the well-being of Lobilio in the paddock before the race.
"Someone called me from the racecourse this afternoon and said that the horse could not win, because he had just seen it in the paddock and it was distressed,'' Coton said.
"A lot of people have rung the Racing Post to voice their concerns that Lobilio was doped and I share their suspicions.''
But Lobilio's trainer, Dai Burchell, said: "As far as I am concerned, there is nothing untoward about the death of the horse.
``I don't know where these rumours have come from. How can anyone say there was something wrong with the horse until it has been examined by a vet?"
David Pipe, head of Public Affairs at the Jockey Club, was unavailable for comment.Reuse content