Police are investigating whether the dumping of a dead koala outside a police station in Victoria's south-west with $50 stuffed in its mouth is linked to a crackdown on drug crime in the region.

Sergeant Jason Von Tunk, who the discovered the koala's body, says he was working alone at the Heywood police station on Saturday night when he heard a thud outside.

He said he went outside to investigate and found the animal dead in the driveway with money in its mouth.

"I went to investigate what it was and I saw a motionless koala in the drive way, and I looked around and couldn't see anyone," Sergeant Von Tunk said.

He continued: "Then I, on closer inspection, saw a $50 note stuffed in its mouth. It's sickening, it's morbid, if it is a joke, it's certainly not funny. I just can't understand it."

Sergeant Von Tunk said he called in another officer from the nearby Portland police station to help establish a motive.

"The money itself, there was no note attached to it or anything, so we can only think that it's some sort of sinister thing, it's rather morbid," he said.

"But without anyone coming forward we're left in the lurch as to who, what, where and why."

But he said the incident could be related to drug investigations.

"There's a number of suspicions I can cast on and none of them have been ruled out, and certainly drugs, but also some sort of protest group or even a prank, I couldn't tell you," he said.

Sergeant Von Tunk said the koala had head injuries but he did not think it was killed deliberately.

"We weren't able to determine how the koala died, but there didn't appear to be any cruelty aspects to it," he said.

"It appears that it could've just been run over and it was an opportunistic way to just get it off the side of the road, put $50 in its mouth and just throw it at the police station."