Defiant Newcastle and Australian captain Andrew Johns has vowed to fight back from a neck injury which threatens his rugby league career.

Johns, the world's best player, stunned the rugby league world on Thursday afternoon when he announced he would miss the remainder of the NRL season and the Kangaroo tour with a bulging disc in his neck.

The 29-year-old will be forced to wear a brace for six weeks and, if that doesn't fix the problem, faces fusion surgery which could rule him out of the game for six months.

And the news could get worse for Johns and the Knights, with Newcastle doctor Neil Halpin conceding there was a slim chance Johns' injury could be career-threatening.

"You have to accept that there is some slight risk of that," Dr Halpin said.

However, a determined Johns was having none of that.

"This is definitely not the end of my playing career," he said.

"I'll be definitely right to play again next year."

Bookmakers reacted swiftly to news Newcastle had lost its talisman, with the club's premiership odds drifting from around $8 to $23.

The Knights, clinging to eighth spot on the NRL ladder, have won just nine games from 24 starts since 1998 without their playmaker.

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