In a statement, MSG says the debris fell during overnight maintenance as workers were cleaning asbestos-related materials in the attic above the ceiling following the New York Rangers' game.
"Out of an abundance of caution, we are postponing tonight’s Knicks v. Magic game. We will be working with the city and independent experts... to evaluate and determine the most appropriate course of action. As the safety of our customers and employees are our top priority, we will not reopen the Garden until we are absolutely assured the Arena is safe."
A spokesman for New York City's Department of Environmental Protection, Farrell Sklerov, said the agency's inspectors were on the scene and had determined that no asbestos had been released.
Garden officials, he said, apparently became concerned after two air quality monitoring stations set up in the arena seating area were triggered while a crew was clearing debris from the building's attic.
Subsequent testing, however, revealed that the dust particles that set off the alarm didn't contain asbestos fibers. The material is only dangerous if it is damaged, produces airborne dust and is inhaled.
The work was done by maintenance staff in the attic above the ceiling following the New York Rangers' game and prevented workers from laying down the Knicks' hardwood floor. The ice surface was still down as of Tuesday afternoon.
In its statement, MSG said it would work with the city and independent experts ATC Associates and GCI Environmental Advisory to determine the next steps.
"As the safety of our customers and employees are our top priority, we will not reopen the Garden until we are absolutely assured the arena is safe," the statement said.
ATC and GCI did not immediately respond to messages left by The Associated Press.
No makeup date for the Magic-Knicks game has been announced. MSG said it would provide information about future events once they have been determined. The Knicks are scheduled to play at home against Washington on Friday. The arena will host Roger Waters: The Wall Live on Saturday, and the Knicks and Rangers will play a doubleheader Sunday.
Should the arena remain closed for a lengthy period, the Knicks might have to look elsewhere to play temporarily. The Izod Center in East Rutherford, N.J., could be considered now that the New Jersey Nets have moved their home games to the Prudential Center in Newark.
Opened in February 1968 and known as "Garden IV," the Garden is in the early stages of a renovation that began last summer. It's expected to cost between $775 and $850 million, with extensive work slated for the summers of 2011 and 2012.
It's the second recent arena-related postponement for the Magic. The exhibition game against Miami that was scheduled for the St. Pete Times Forum in Tampa, Fla., was canceled because of slippery court conditions after arena officials said an oil-based cleaning solution was mistakenly applied.