An investigation is under way at Newmarket Racecourse after a pane of glass fell from the main grandstand and shattered onto seats below.
The area would normally have been packed with racegoers, but thankfully all meetings at the moment are being held behind closed doors.
The incident occurred at Thursday's meeting, the first of four days on the Rowley Mile.
Although crowds are not permitted to attend, the fixture is particularly significant as it hosts horse racing's first Classic races of the season, the Qipco 2,000 and 1,000 Guineas.
The prestigious contests, on Saturday and Sunday, come at the end of the first week of the sport's resumption, which began at Newcastle on Monday.
Amy Starkey, who runs Newmarket as East Regional Director for Jockey Club Racecourses, said the incident is being probed.
“A window fell out of the Champions Gallery on the third floor on to the level two seating for no explained reason," she added.
"We are now investigating why and how it’s occurred.
“Clearly it is very concerning and thankfully we are staging racing behind closed doors so no members of the public or our team have access to the area.”
Pictures show the large hole left in the grandstand's glass frontage by the missing pane.
Workmen were seen clearing it up, as the card of ten races went ahead with winners for top jockeys Frankie Dettori and Oisin Murphy.
On a normal raceday, the Champions Gallery restaurant is used for entertaining racegoers, with packages from £144 per person.
