"The pressure inside is building up more and more, and at some point the animal could explode with a huge bang," whale researcher Fabian Ritter told dpa.
"Such a situation is almost inevitable."
Ritter, a member of the scientific committee of the International Whaling Commission and author of several books, said similar incidents had been documented in the past.
In one infamous case in 2004, a sperm whale exploded while being transported through the southern Taiwanese city of Tainan for a post-mortem examination, spraying blood and internal organs across the street and nearby buildings.
"You would not have wanted to be standing in that rain of blood, particles and decomposition gases," he said.
The German marine biologist said the risk of an explosion could have been reduced by puncturing or cutting open the bloated carcass.
However, in the latest case off Denmark, such an intervention should have taken place much earlier and would now already be risky, he said.
Images of the humpback whale, nicknamed Timmy, showed its throat pouch had swollen dramatically like a balloon, Ritter said.
He added that the situation could also resolve itself if a natural tear formed in the tissue, allowing gases to escape without an explosion.
Timmy was discovered off the Danish island of Anholt on May 14.
It was later confirmed to be the same whale that first stranded off Germany's Baltic coast in late March before being moved by rescuers about a month later into the North Sea.
The saga made headlines around the world.
Danish authorities said they could attempt to transport the whale carcass to the mainland early next week.
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