The spinal specialist who convinced Andrew Johns to hang up his boots believes there is no need for a mandatory scanning of every NRL player in relation to neck injuries.

Professor John Yeo, head of the Royal North Shore spinal unit in Sydney, said subjecting every player to a mandatory x-ray or MRI scan would be unnecessary.

"I don't think that that's justified unless there's symptoms suggesting there might be some abnormality, and not necessarily symptoms relating to the bulging disc," Professor Yeo said.

"As in Joey's case, the symptoms were essentially a damaged joint."

Johns pulled down the curtain on his glittering 15-year career after being diagnosed with a bulging disc in his neck.

The bulging disc was not causing Johns pain at the time, but was discovered when the former Test captain underwent an MRI for a facet-joint injury in his neck.

But rather than suggest every player undergo scans, Professor Yeo said he would strongly suggest any player feeling any pain in their neck to be checked out.

"If you're playing now free of symptoms and doing it very well, then I don't think it's necessary to race out and x-ray everyone playing rugby league, but I do think that if you had a neck injury or you did have susceptibility to neck pains of one sort or anther, you need to have a thorough examination or investigation," he said.

"The important message in all that is if you do have symptoms, get them looked at so that you don't come back onto the field and play and have a problem that hasn't been looked into.

"If attention is drawn to a part of the body that isn't working well then you need to investigate it and consider all the possibilities."

Speaking on Sydney radio, Knights doctor Neil Halpin said it was quite possible that there were players running around in the NRL with undetected bulging discs in their neck.

But Dr Halpin too refused to push for all players to be scanned.

"There is a line of thought that we should," Dr Halpin told radio station 2KY.

"A case can be made for it. Whether that is a good idea I don't know.

"That's something a panel of experts could look at."

Halpin said that in Johns' case the injury was down to wear and tear, but was not related to the bulging disc which almost brought a premature end to his career in 2003.

"That (the previous bulging disc) has healed but he has developed another one at a different level," Dr Halpin said.

"The present disc injury is more severe and it is one below the original one which has now healed."

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