A member of the public dressed as a jockey had to be escorted from the paddock at Newbury on Friday, where the Queen was in attendance.
The man, believed to be on a stag party trip, was spotted by Newbury's chief executive Julian Thick before the first race and led out of the ring.
Her Majesty, celebrating her 91st birthday, was at the Berkshire track to watch Maths Prize, who could only finish fifth of the six runners in the Dubai Duty Free Golf World Cup EBF Stallions Conditions Stakes, which was the third race on the card.
While it eventually appeared to be a case of nothing more than high jinks, with the Queen present it was an incident the course could have done without.
Newbury's head of communications Andy Clifton said: "A guy who appeared to be on a stag do tried to walk into the parade ring with the jockeys, but he was politely asked to leave by Julian Thick, who apprehended him.
"There was nothing sinister about it, but when the Queen is here these things need to be taken seriously."
The Queen was not in the area at the time as she was having lunch in the royal box.