Owner Annette Edwards told The Associated Press on Wednesday that Simon, a 10-month-old, 3-foot-long continental rabbit, had a vet check shortly before travelling from Heathrow airport to Chicago's O'Hare airport. The distraught breeder, who hails from Worcestershire, said Simon had been purchased by a celebrity whom she did not identify.
"Simon had his vet check just before getting on the plane," she said. "He was fit as a fiddle."
The airline said in a statement that it was "saddened" by the news and had been in contact with Edwards and offered assistance.
"The safety and wellbeing of all the animals that travel with us is of the utmost importance to United Airlines and our PetSafe team," the airline said.
Edwards said the airline was examining CCTV images to determine what might have happened to the rabbit. United declined to comment on the matter beyond its statement.
According to the U.S. Department of Transportation, U.S. airlines reported 35 animal deaths in 2015 (which is the most recent data available). The same report shows that 14 deaths happened on United flights.
That year, the airline carried a total of 97,156 animals. The rate with which these types of incidents occurred (2.37 for every 10,000 animals transported that year) is the highest among all U.S. airlines.
United is currently dealing with public relations issues after a passenger who would not give up his seat was forcibly removed from a plane in Chicago earlier this month. Airport officers removed David Dao, a 69-year-old physician from Kentucky. Images of his bloodied face were widely circulated on social media, forcing the airline's CEO to apologise.