The shocking moment Sydney police found a man bound, gagged and left for dead

Police have encountered one of their more bizarre cases, finding a man bound, gagged and left for dead in Sydney parkland.

The reason why is still a mystery.

Police found the man just before 12.30pm Tuesday afternoon off Captain Cook Drive in Willmot.

Paramedics treated the victim at the scene before he was taken to Blacktown Hospital with non-life threatening injuries.

The man, who is believed to be in his early 20s, had been bashed and was possibly drug-affected.

A witness who emerged from bushland told police he saw the man get dumped from a blue Commodore, which was found nearby.

Police questioned three young men and took them into custody after an onlooker saw them leaving the area.

They had been responding to reports of a car doing burnouts in the area when they spotted the man.

At this stage they don't believe the car hoon and the bound man are connected.

The father of one of the men questioned denied his son was involved.

The area was cordoned off with forensic examiners bagging evidence as they try to solve a mystery they stumbled across by accident.