Despite an intensive search of several different parts of the rainforest, Mr Williams has failed to find a single possum.
"It was quite depressing going back on the last field trip a couple of weeks ago, going back night after night thinking ok, we'll find one tonight, but no we still didn't find any," he told the Australian Broadcasting Corporation.
"We tried several different areas. We did quite an intense effort without finding a single individual."
But Mr Williams said he was still "a way off" from proving the animal had become extinct.
"The fact that it has declined to such a degree that we can't find one suggests a very serious impact regardless of whether it's actually completely gone extinct," he said.
"If they have died out it would be first example of something that has gone extinct purely because of global warming."
He predicted several other native Australian animals would find themselves in similar predicaments to the "Dodo of the Daintree" in the coming years Australia has a bad track record when it comes to protecting its native animals.
In the country's most notorious case of species mismanagement, the Tasmanian Tiger, or Thylacine, was allowed to disappear. In 1939, after the animal had been hunted to near extinction, the last known tiger died of exposure on the concrete floor of a wire cage after its keeper forgot to lock it up for the night and it died of exposure.