Hastings police were still trying to piece together how the man got there.
"He's been found on that stretch of State Highway 50A and basically we don't know what's happened," Acting Detective Senior Sergeant Mark Moorhouse said.
"His injuries are consistent with being either hit by a vehicle or thrown out of a vehicle, but until we have more information, we can not confirm anything."
State Highway 50A was cordoned off at the Omahu Rd roundabout and Flaxmere Ave for about an hour yesterday while the scene was scoured for clues.
Hastings police serious crash unit initially attended the incident but passed the case onto their Criminal Investigation Branch (CIB) for further inquiry.
A team of detectives are currently looking into the incident, though it was difficult to pin point what happened without any witnesses.
"There's three likely scenario's: 1. he's been hit by a vehicle, 2. he's been thrown from a vehicle or 3. something has happened to him elsewhere and he's been dumped there," Mr Moorhouse said.
"We are appealing to anybody who may have seen what happened to come forward with that information."
A scene investigation and subsequent interviews with the injured man shed little light on what happened to him or how long he had been there.
"We have only been able to get limited detail from him."
Police hoped to speak with the man again today to get a clearer picture of how he ended up on the side of the expressway.
Anyone with information can call Hastings police on 06) 8730500 or crimestoppers 0800 555 111.
