Jam And Mam was prevented from running at Doncaster on Sunday after one of the members of staff travelling with the horse failed a temperature check.
Strict protocols in place on racecourses since the resumption of racing in Britain in June 1 mean all individuals attending a fixture must pass a temperature check, with a threshold of 37.8C.
The Archie Watson-trained three-year-old had been due to run in division one of the Read Andrew Balding On Betway Insider Handicap.
A spokesperson for the British Horseracing Authority said: “Following arrival at the course, one of the members of staff travelling with Jam And Mam failed to meet the screening requirements to enter.
“In order to ensure that behind closed doors racing is as safe and secure an environment as possible for all attendees and minimise any risk of spreading Covid-19, those travelling with the horse were not able to enter the racecourse and as such the horse was declared a non-runner.
“This is in accordance with the protocols developed with organisations from across the racing industry, which are designed to safeguard the health of all those attending.”