Officials at Newmarket believe a chemical reaction could have caused a pane of glass to fall from the main grandstand at the track on Thursday.
Racing was taking place behind closed doors for the first time on the Rowley Mile since the resumption of racing, with the glass falling into the seats below which would usually have been full of spectators.
Amy Starkey, who runs Newmarket as East Regional Director for Jockey Club Racecourses, reported investigations to be ongoing and the area has been cordoned off until the issue is resolved.
She said: “An investigation was started yesterday and will continue today about the cause of the window falling out of the Champions Gallery restaurant.
“Early indications after inspecting the broken glass are that it was a chemical reaction and we may have to put a protective film or glass over the whole frontage.
“We have cordoned off the area to keep our staff and others safe, something that will stay in place until the problem has been solved.”