Victorian man Milan Lemic vanished on December 22 after walking away from his bogged ute at Bairds Crossing near the Upper Daintree village.

Police found him alive on Monday after a motorcyclist said he'd twice spotted a man on the rugged Creb Track - a 4WD-only track that's currently closed due to water levels.

"We cannot confirm at this time that this is a remarkable story of survival," Inspector Denis Fitzpatrick told reporters in Cairns on Tuesday.

"It could well be a case of active avoidance for some time - from police, and other authorities like the SES who have volunteered their time and energy to try and locate this person."

Insp Fitzpatrick said there was concern for Mr Lemic's mental health and he'd been taken to a safe place as detectives wait to interview him.

He was not wanted by police for any reason, and the inspector said the entire episode was difficult to explain.

One avenue of inquiry is likely to be whether the 29-year-old was helped by anyone during the time he was missing.

"That is a firm possibility, and that will probably be a tangent of investigation to explain his survivability and level of health in these conditions for well over three weeks," Insp Fitzpatrick said.

Mr Lemic has not told police much about the weeks he was missing, but did say he survived by eating berries from the rainforest.

He did not try to run from police, who used all-terrain vehicles to reach him.

"Physically (he was) very dishevelled. We have concerns for his mental stability. We're hoping that his condition will improve so we can get a confirmed version from him."

The search for Mr Lemic has been mired in mystery from the start.

On the day he vanished, a passer-by noticed his bogged ute and offered to go and get a tractor to pull it out.

But by the time the Good Samaritan returned 20 minutes later Mr Lemic had vanished, sparking initial fears he may have been taken by a crocodile.

During the long running search there were also what police called credible but unconfirmed sightings of the Victorian.

Mr Lemic's mother Yana travelled to Cairns last week and made an emotional appeal for help to find her son, including a direct appeal to him to "please just let us know that you are OK".

Insp Fitzpatrick said the family was enormously relieved to learn on Monday night that he was alive.

Australian Associated Press