Visitors were stunned by a loud crash when the pane fell from the roof, showering the area with glass, at around noon yesterday.
Council officials said contractors were inspecting and cleaning downpipes when the incident happened.
Broken glass was strewn across the visitor attraction and an area was cordoned off while the debris was cleared.
The glasshouse, which contains tropical plants, was busy with families, including young children, when the pane crashed to the ground. No one was injured.
One mum, who did not wish to be named, said: "If it had landed on someone there's no doubt they would have been killed.
"It really is astonishing that nobody was injured. The glass has obviously fallen from a great height and there were hundreds of bits scattered all over the Winter Gardens.
"There were shards of glass everywhere – I picked up about 20 bits of broken glass while I was sitting in the cafe area.
"The workers were saying 'don't let your children play on the floor because of the glass'.
"It's really quite scary to think what could have happened."
The Winter Gardens, which are attached to the People's Palace, attract thousands of visitors every year.
A spokesman for Glasgow City Council said: "A pane of glass was broken while contractors were inspecting and cleaning downpipes. Nobody else was in the vicinity and there were no injuries."