The chief executive of World Rugby is "extremely worried" about the Six Nations if crowds do not return.
And Brett Gosper told BBC Scotland that some unions will go bust without government help, possibly by the turn of the year.
Gosper estimates the Six Nations will lose more than £100m if paying fans are excluded from matches.
"We hope that broadcast funding can be sufficient to keep the unions going through the Six Nations," he said.
"But, ultimately, if things don't start getting better by springtime, we are going to be in a more drastic situation."
The 2020 Six Nations tournament is due to be concluded next month, with Ireland hosting Italy on 24 October and three remaining fixtures - Wales v Scotland, Italy v England and France v Ireland - played seven days later.
Autumn Tests are being replaced by an eight-team tournament in which the Six Nations sides will be joined by Georgia and Fiji.
However, sports governing bodies in the UK are preparing for no spectators throughout the winter as coronavirus cases continue to rise.
World Rugby has been providing money advances to support unions but Gosper said "we are well into the red zone" in terms of funding, adding: "We know that going into next year money will run out.
"Unions will be looking very strongly for government support to ensure that the game is maintained.
"Each union will have their cut off point. I can't share details of every union but for many this will become very difficult in the early part of next year."
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